After the fall of 38 Studios (The folks behind the ill fated Copernicus MMO), One man wrecking crew Joe Mirabello set off on his own personal venture to make a game by himself. Over the last eighteen months and utilizing Ureal Engine 3 he took old school twitch first person shooter gameplay and fused it with roguelike sensibilities such as perma-death and random levels and enemy spawns. He calls his creation Tower of Guns.
On top of classic run-and-gun shooting you can level up your weapons or purchase upgrades using currency dropped from fallen enemies. Though the game can be beaten in 45 minutes to an hour, it is not an easy game by any means. There are plenty of unlockables and secrets to be found including many new guns and perks to equip (such as triple jumping).
Tower of Guns is built with replayability in mind and if you enjoy a challenge while frantically shooting at things such as large robots and guns then I can safely say it is more than worth your time. The game can be purchased via Steam or directly through Joe's website.