Any PS3 owners here play Demon's Souls? I picked it up on sale a couple weeks back. It has difficult, unforgiving gameplay, but not in a cheap way. When you die, it's because you screwed up. I'm not usually into action RPGs--most of my combat time in Fallout 3 was spent in V.A.T.S.--but once I got the hang of it, I started to enjoy it.
The other game that's been occupying my time is, of all things, Angry Birds. I've been playing the iPhone version, but it's available for other mobile platforms. Pretty addictive and challenging puzzles with great cartoony graphics, sound effects, and physics. For 99¢, it's a no-brainer.