The main issue I'm hitting with it right now is that a whole lot of the UI is really unintuitive and they don't really explain things. Tooltips don't appear where there should really be tooltips and often when there is some explanatory text it's in such poorly translated English that it's impossible to really know what they're saying.
Beyond that, it's spectacular and I'm so close to just paying for it and killing a WoW account... I have two of them, you see. But I felt that way about Oblivion too. I played the hell out of it for a month and then can't get back into it. It looks great, it's wonderfully open ended... I just can't care about it. Which sucks because I want to finish up the main quest line and play the expansiony bits.
But the most hardcore thing I've done lately gaming wise, besides finding a way to run Heretic (a game designed in DOS on the original Doom engine) on my 64bit Vista computer is installing You Don't Know Jack. FUCK YEAH COMPUTER TRIVIA GAMES. WHOOOOOOO
I'm going to go kill 200 "Rusty Fanatics" now. They sort of look like a combination of an actual scarecrow, a thing with enormous knives growing out of their forearms instead of actual hands (I think it reminds me of a monster in a game or movie but I can't place it), and Mr. Crow from Unreal Tournament 2004 (because they are totally wearing top hats).