Alright folks, I've had a chance to play GSB, and I have to say that I LOVE it. It is a niche game, however, and its target audience are the people who loved customizing Mechwarrior loadouts before a fight. That's me, so I fell in love with this game.
It really is addictive, and if I'd known how fun it was beforehand I would've gladly paid $20. You can get your money's worth of replayability and fun out of downloading user-created fleets and fighting them. They're generally tougher than the single-player missions.
Essentially, it's a puzzle game. You're matched against an enemy fleet and need to determine how to beat them, ideally with the weakest force you can field. It might be strong on cruisers with tough shields, weak armor, and short-range weaponry. So, you change your own cruiser loadout to utilize Mk. XIV Shieldbreaker Plasma Uber Neutron cannons, boost the engines so they can better stay out of enemy range, and equip your fighters with Mk. III anti-armor rockets and have them attack the enemy cruisers from within their own shields.
You get the idea.
After the battle, there's a TON of stats that can be manipulated in a bajillion ways, so you can determine exactly how much damage Fighter Squadron 'Reaper' did to an enemy cruiser, what percentage of shots hit, how many shots were ineffective due to enemy armor, etc. Then you tinker your loadout and try it again.
There isn't a campaign yet - that's coming later this year, I think. The SP game consists of a whole bunch of pre-made missions to get through, that unlock newer, different ships, new races, weapons, armor, mods, etc.
Anyway, if you like the idea of waffling over using a .24 fire interval beam laser vs. a long-range megaton launcher with decoys, then get this game. It's one of the BEST in its category (actually I can't think of any others!). It's also great to be supporting an indie dev who's very active on both the Steam and his own forums.