This afternoon I decided to try out the OSC (part1) rules in a quick solo game. 50 page of rules with a lot of pictures were quick enough to read trough and as I have said before the layout in both normal form and optimized for landscape screens with hyperlinks is very nice. Forgive the unpainted models and simple terrain, like I said this was more of a test than anything. The game is written with 28mm in mind but suggests playing 15mm with CM instead of inches.

I played a 100 point game in 15mm, my table was actually pretty large for this game. You could play a 75 point 15mm game on a 25x25cm table. You could play this on a shoebox. I like this.
In OSC the most important stat of any model is its level, going from 1(civilian) to 7 special forces. By far most checks in the game consist of rolling a d10 adding your level and getting 10 or higher. There are very few modifiers instead you might get a re-roll of failed dice.

My force consisted of a professional soldier (lvl 5) group of four, a commander, two riflemen and a sniper, all wearing superior ballistic armour and carrying LMG's. I used Rebel minis Titan marines for them, their weapons are big bulky and have a large box mag so the LMG sounded appropriate.
The opposing mercs were trainer soldiers (lvl4) wearing basic armour and mostly using assault rifles, they had 5 riflemen, a commander, a designated marksman with DMR and a "blockhead" power armour trooper (lvl 5) in enclosed hard suit armour with a auto shotgun. The troops are from rebel again, the blockhead is from critical mass games.
Stating models is pretty quick and easy, you pick a level, armour and weapons and you're done. The rules are clearly aimed towards near future and further, enclosed hard suits (power armour) is supported as are counter measures. In fact one of the example forces consists of just these. The book includes a good selection of modern weapon,s including (cross)bows all the way up to multi barrelled rocket launchers. There are 5 types of close combat weapons as well. The book has mechanics for energy weapons and rather deadly looking fusion drive weapons, however there currently is no way to actually use these. More on that later.

The deployment and objective rules are simple but instantly hooked me. You place the main objective at the centre of the table, and scatter 4 secondary objectives 1d10 from there. Both sides roll for their personal objective, which there are 6 of. In this case the Soldiers were trying to return the objectives to their deployment point and the mercs were trying to keep the main objective under their control and in its original location. Very clashing objectives already.
Rather then placing your models you place your deployment point (DP) a credit card sized slab. I imagine this as the back of a APC or having a VTOL hovering above it, but its a bit abstract. You put this somewhere on the table. The rules state that smaller groups, on average, only notice each other later then larger ones so the distance you need to keep from things depends on the size of the game. (very nice idea!) In my case at 100pts 10" from the objective and 20" from the enemy. at 500+ games this goes up to 20"and 40" respectively.

No IGOYGO here. The game uses alternating activations, but its more complicated then that. When its your activation you get 2 actions, you're allowed to spend these on one or two models. If you activate your commander you get an additional action. There is also no differentiation between the actions, your commander can spend 3 actions firing his full auto weapon.
So why would you split your actions? There is the options of suppressing an enemy before moving another but more importantly you are never allowed to have two activations in a row, if this would happen the turn ends. So both players have roughly the same number of actions to use, even if they have a different number of models. If you have the initiative and a larger force you get 2 actions more, but that's it. Important to note, if a model took an action during a activation it gets marked as activated and can't act any more during the rest of the turn, so splitting your actions does tie models down. I think this is where the meat of the game lies.

Combat is pretty simple, using the d10 mechanism described above. All weapons also have a rating at which point a normal hit becomes a lethal hit. For assault rifles this is 9+ weapons can shoot over their normal range reducing this lethality with 1 for each 10" over range. Doing a single shot doubles your weapon range but you only throw a single die. When firing auto you can throw 2-5 dice and resolve them separately. Big downside is that every 1 you throw jams the weapon, simulating both actual jams and running out of ammo. Normally a jam nullifies all other rolls in that attack, so going full 5 dice on a assault rifle is at risk of jamming up. The LMG's of my soldiers had the box magazine ability which meant that jams still happened but didn't nullify the other shots in the group.
The are alternate options for blind shooting, which allows you to move 1" before and after the shot, returning to total cover if you wish, however this is likely to only suppress rather then wound. You can also hip shoot allowing you to move d10 and shoot up to 10" another option for suppressive fire and double tapping at short range (increasing lethality)
When shot you have the option of trying to avoid the shot, if it came from your front arc and there is any sort of obstacle obscuring you. (or you were on alert, having spend an action before to so so) The evasion roll is a simple d10 check with your level again, a straight up 1 is going to kill you and any hits are still going to count as suppression. Alternatively there is the option to rely on your armour. The rules claim there are no modifiers, only re-roll in the game. This is true, but in the case of armour you do determine your save by comparing it to the weapon. Basic weapon vs Basic armour gives you a 4+ save on a d6. If your armour is "fully enclosed" like my blockhead you use a d10 instead but your arc of sight is reduced from 180 to 90 degrees. Successful armour saves turn hits and lethal hits into suppression.

I keep mentioning hits, lethal hits and suppression. So how does that work. Lethal hits kill models in one, as the name suggests, evasion turns lethal into normal hits, armour reduces it to suppression. You can take a number of normal hits equal to your level, which I mentioned way above. If you are suppressed you need to take a check (d10+lvl) or the action you were trying is wasted. If you gain more suppression then your level the overflow become hits. This is important, since MG's have the suppression rule that give you 1d6 extra suppression on any hit. My power armour rushed a group of enemies hoping to catch them all with his auto shotgun, rolled a 1 for his shooting and despite saving all hits with his armour he died from overflow suppression.
Suppression figures into almost any action of the game. You can spend an action moving up to 6" or designate a point and sprint 2d10 towards it. However rolling a 1 gives suppression while a 10 removes it. So how do we get rid of suppression? Your commander can spend an action to remove all suppression from all models up to twice his lvl away. Or you can have a model "man up" which can both reduce suppression and hits, but a roll of 1 results in the model deserting. You can have the model retreat with an action, moving 2d6 towards their DP and reducing suppression by the highest rolled d6. I love this idea, retreat is a viable and useful tactical option. And again with surrender. You can respond to CC by surrendering and you can also challenge a model up to 3" away to surrender. Surrendered models become hostage tokens. If you accompany a hostage to your DP you can get a re-enforcement by replacing a previously removed/killed model. This works both ways, you can use hostages form both sides to return models to play. Capturing rather then killing is a useful choice.
Much like hostages you need to bring the objectives to your DP. But what if the DP is too far away? Your commander can spend an action to change the location of the DP. IT still needs to comply to the distance rules mentioned before, but there are a number of interesting tactical options. One of my commanders made a mad sprint for a distant objective one turn, then picked it up, placed the DP in a near location and delivered it the next turn. Models are not deployed at the start of the game, and you might have fewer activations then your opponent. So a larger force might actually deploy half its models, including the commander in the first turn and then in the second turn re-deploy the DP and have the rest of their force perform a pincer move from a different spot. This is why I imagine the DP having a VTOL hovering over it.
So to me at least that all sounds very cool and interesting. Now here is a big downside. This is part 1 of 4. The books contains rules and options you actually cant use use. There are actions for medics, radioman and weapon teams, airstrikes and IED mentioned however the rules in part 1 do not cover the deployment of these models. Like I said above the same goes for the energy weapons. part 2 of the rules will fix part of this, with the extra model types, vehicles and drones, as well as fire-team movement for much larger games.
Part 3 should slap on the full sci-fi with extra vehicle movement types (I expet walkers and grav) and a lot more weapons and further model customization for aliens and sci-fi weirdness.
part 4 is supposed to include campaign rules, solo play and the mechanics for creating your own weapons and their point costs, as well as further toolkits.
I can say part 1 really is a solid slick skirmish game, playing very quick but detailed with as few as 4 models a side but would probably also do fine at 15 a side. You might want to get a micro dice like I did, since every model is liable to get hits, suppression and multiple jams at times. Beyond that there are states like alert and gone to ground, so on table book keeping is quite high. There is a number of smaller rules that really add flavour, such as models being able to climb an extra inch if they have somebody next to them at the bottom or top. Or grenade types which can be fired from launchers, including the bow types.
The example forces include your typical modern army, a hardsuit marine squad, a mixed group of both, your typical robed insurgents with 47's but also a group of post apocalyptic style reavers made from woodland Indians.
I am very positive about everything that's in these rules, and very hopeful for what's next since I do want to field some more specialized things. With a PDF at 4 pounds I think there are a lot worse choices out there, and if all 4 parts have the quality of the first this might actually end up the best skirmish level sci-fi game on the block.
EDIT: like Mr. evil pointed out, I forgot to mention the card mechanic. Basically you get a card when you loose the initiative roll, you must play this card in the current turn or discard it. The pile of these cards functions as a turn counter. Additionally the player who has the least points, (unable to fill those last few?) gets a free card at the start of the game and your commander can spend an action to get a card, which he needs to play directly. So no large hands of cards to keep track of. The cards are also pretty simple for the most part. They are split into 3 piles and you must draw from a different pile each time you get a card. Resources are about removing suppression hits and jams, action cards let you take a particular action for free and the event cards manipulate the battlefield or enemy, limiting LOS, jamming a weapon or model or having it chased from a building by an angry resident.
My opinion on the cards is mixed. You have 2 cards at most at any time, so there is no complicated card play, but all the cards can be life savers (or takers) if played at the right time. During my game the first card allowed me to remove Jams where there were none, the second allowed a free go to ground action which was useful but nothing mayor, the third allowed the placement of a temporary LOS and movement blocking piece which was a mayor part of tactics that turn. I have to say, that last card was a mayor game changer and very interesting.