How is it?
I bought it because I played a game at Attic Attack I, and liked the mechanics a lot, so, obviously, I think the rules are rather good.
Theres a lot of stuff about generating terrain that requires a LOT of terrain to pick from, so I'll not be using that a whole lot ohter than for inspiration - and also some 'Habitat'-rules with monsters attacking your units if they come too close, which are fine for spicing up things now and then, but, frankly, won't see much use, because - once more - it requires a lot of extra minis to be bought and painted, and I like to focus on my armies instead.
The simple movement and combat rules are what realy makes this game worth every penny. If you have ever gone grey-haired trying to manouver a Warhamster unit into position for making that decisive charge, you'll simply LOVE this set of rules. Don't take my word for it, buy the rules and see for yourself

If you've tried SAGA, you'll have a hint of how a unit behaves during movement. Very easy, very simple, and it WORKS!
Combat is very simple, too, you roll a d6 for each warrior fighting, have to score a set value to hit, and your opponent gets 1d6 for each warrior to roll for his defense, saving on a set value. The unit that takes most casualties recoils away from the enemy, unless it has an ability that prevents this, in which case the units are locked in combat.
EDIT:
A unit only recoils if it is 'loose' (not 'formed - i.e. in 'skirmish' formations as opposed to 'tight' rank-and-file formation). Formed units do not recoil.
And the ability that allows 'loose' formations to not recoil is called 'tenacious'
/EDIT
You can play a fairly large battle in about 2 hours (including set-up). and the army lists (included in the book), with not much tweaking, easily allows the use of your existing armies for other game systems. You can use single based or unit based models, it doesn't matter to the mechanics.
On top of this, we have a growing GoB15mm community here in Denmark (we simply halve all measurements), which was another motivating factor for getting the rules - although I intend to play the game in 28mm with LotR minis, I have been eyeing Mark Copplestones 15/18mm range for a while, and I think my 15mm army will be a combination of barbarians and dwarfs.