Fast paced and intense shooter with a great metal soundtrack. The game does become a little less interesting when you become overpowered with upgrades.
Great combat and abilities once you get to that stage in the game. Before that the hordes aren't fun to encounter and after they're a joke. Boss fights were easily the best part of any game I've played.
An FPS which plays more like a puzzle game is a welcome surprise. Main story has more than I thought it would and the endless more is fun to come back to.
Flipping gravity makes you think about the puzzles in a very different way to a normal platformer. Quick respawn time makes it easy to get back into quite a hard game.