Android Central

The guys behind the venerable Tank Hero game have launched their next title on Android called Sector Strike. It's a free-to-play sci-fi shoot 'em up with all of trappings of classic 2D spaceship games. You move your ship around to evade enemies while holding the trigger down on your guns and picking up credits from their wrecks to spend on upgrades. Players gradually work their way through new sectors, provided they survive the withering hail of plasma fire from a wide range of crafty foes. 

I've played a little bit on my Nexus 7 and the graphics are buttery smooth, the gameplay is challenging, and the controls are very responsive. Yeah, they offer in-app purchases for accelerated progress, but it doesn't feel like there's anything you can't get just by playing the game a whole bunch. As far as casual, old-school pew-pewin' on Android goes, Sector Strike is looking very promising. Check it out.