Super Crate Box is good fun in a very retro way. It's a platform shooter in which score is dependent solely on collecting crates -- and each crate contains a gun. There are quite a variety of guns, but you have no control over which you possess at any given time, since each time you get to a crate, you get a different one.
Enemies spawn from a drop point above; you can evade them by jumping from platform to platform, but once they reach the bottom of the level, they fall down, reappearing at the top of the screen, and are now red and fall faster. Since more and more enemies spawn over time, you want to kill them as frequently as possible lest you become overwhelmed.
While there are only three levels in the game, the sheer variety of weapon and enemy types, the random spawn locations of new crates, the frenetic nature of the gameplay, and the crispness of the controls combine to produce an enjoyable little title reminiscent of the arcade; you're lucky to survive beyond a minute or two, and can imagine the need to insert the next quarter.
In a nice touch, new weapons and enemies are unlocked over time, but are gated by the total number of crates collected in all plays, so the nature of the game (and its difficulty) changes over time.
Super Crate Box was a 2011 IGF finalist in the Excellence in Design category.