If you're looking for a dungeon crawl/hack 'n slash type game and don’t mind side scrolling I'd recommend Muramasa: The Demon Blade. It's set in a feudal Japan type world and has a real SNES/Genesis feel with excellent visuals. Depending on the difficulty chosen, you can mindlessly hack 'n slash on easy, or play the harder difficulty which requires more precise timing and better execution. Then if you're a glutton for punishment and beat the harder difficulty you can play again on what the game calls Shigurui mode. In Shigurui mode you basically play hard again but with only 1 HP.
RPG wise I'd go with Fire Emblem: Radiant Dawn. It's a turn and grid based strategy RPG. If you not familiar with the series it can be hit or miss with some folks due to some quirks. The quirks being... All combat is completely automated. It's got a steep difficulty. Death in this game is permanent. All characters you recruit are unique, which is cool except for when your favorite character dies.
As already mentioned the new Metroid is sweet.
