Based on my experience with Rogue Stars, I think there are two main things that put people off.
First, there are a few example characters and crews statted up in the rule book, but nothing really “general purpose”, so the players have to sink time into creating profiles for every figure they want to use. In my case, my opponent was my kid, so I ended up spending a lot of time coming up with profiles before we could have a game.
This rings true. I think Rogue Stars is a good game, but it has a much longer "time to table" than Andrea's other games. My son really likes the game, but we play Mutants and Death Ray Guns much, much more often, because we can get a game of that going in five minutes.
Which brings me to the second thing - Rogue Stars added a lot of chrome/finicky details onto the SoBH game engine and it plays much more slowly. I played lots of SoBH with kiddo and we like how fast it plays; it feels cinematic. At the end of our first game of Rogue Stars, kiddo said to me, “you know, if we were watching a movie where that game was a scene, what we took an hour and a half to play would have been two minutes”. The second game was much the same, with a different scenario - not very cinematic.
Again, I agree. Where Rogue Stars excels, I think, is in creating a really detailed, tense firefight. And that does entail taking minutes to play seconds. It can be very rewarding, with lots of risk/reward decisions as characters are pinned and fatigued, but it's a different feel from most skirmish games. I sometimes wonder if it would work best in a series of linked 'scenes', almost like RPG encounters.
Mutants and Death Ray Guns is a really nice sci-fi ruleset. Oddly, it doesn't seem to be played nearly as much as Song of Blades. I wonder if that's because of the post-apocalypse tag. If so, it's a shame, because the rules work really well for all kinds of sci-fi (just ditch the weapon and armour jamming if you want technology that runs more smoothly). There are a few subtle but important changes from Song of Blades that make it work very well for sci-fi.
All the enthusiasm for Galactic Heroes prompted me to buy that last night; it looks very interesting - possibly occupying a similar sort of space to Mutants and Death Ray Guns. Of the two, GH is perhaps a little more accessible and MDRG a little more detailed - though also with slightly simpler core mechanics. I look forward to a game or two so I compare it with MDRG. The big difference, from an initial read-through, is that MDRG's optional points system allows you to build in more asymmetrical sides that are still well balanced (e.g. three space marines on one side against a dozen lower-tech scavengers on the other). Galactic Heroes assumes a five-a-side starting set-up, though the Grunt and Horde rules allow you to tweak this a bit. That said, the non-points system in MDRG assumes roughly five a side (and random generation).
Both games use the 'traits' set-up that seems to be a real
bęte noire for many people. I've never really understood this, as the MDRG/SoBH traits are very easy to memorise after a game or two. Galactic Heroes looks to be much the same here - the kind of game where you don't really need the rulebook after a couple of run-throughs. That's a big positive in my book. One point of difference might be that MDRG can be run with most characters having no traits, whereas GH assumes that everyone has at least one.