We love Super House of Dead Ninjas. It's the follow-up to developer Megadev's well-recieved House of Dead Ninjas, and improves on its predecessor in almost every way. In case you're not familiar with the original, you played as a lone ninja, trying to find your way to the bottom of a seemingly-endless randomly-generated tower, fighting enemies and collecting time power-ups as you race against the clock. The sequel features a big visual upgrade, but it's the gameplay that's seen the most significant change here.
While the tower is still randomly generated, there are now specific enemy groups for each sector, separated by boss fights. You can also unlock new weapons and magic spells, which are all pretty balanced — each has its own positives and negatives. Gameplay is a little more forgiving now: you'll start the game with two 'continues,' and when your time gets low you'll be chased by the reaper, rather than dying instantly. However, the tricky boss fights and increasingly chaotic gameplay will have you seeing "Game Over" often enough. Head over to Adult Swim to try it out for yourself, but be sure to read the excellent in-game comic before you start playing.