Tower of Guns is an excellent game, comparable to Unreal Tournament, but combined with Borderlands-esque graphics.
The game features a variety of weapons, lots of movement, and plenty of enemies to shoot at. Oh, and permadeath. Can’t forget the permadeath. You’ll find yourself running (more jumping than running, actually) around the various arenas shooting away at all sorts of foes with a large assortment of weapons. I do wish a multiplayer mode was implemented, however. The game is fun in singleplayer, sure, but it’d be so much better with a friend.
There’s even random map generation, which is awesome, but although it may seem random, there isn’t much of a variety provided. Even so, I did enjoy my time with Tower of Guns and I can recommend it.