Just a heads up, the GOTY edition was released today. Went and picked up mine. I started a new game a couple of weeks ago on hard, I'm lvl 19 working on the main quest going through Little Lamplight.
One thing I noticed about playing on hard is you level up faster then before. I really don't like that, cause once I hit the level cap I don't feel like playing any more.
I haven't played any DLC yet and I still think this is the best game ever, IMHO. I never replay games, but I'm on my third round with Fallout3, I can see myself playing it again soon too. Totally evil, poking people in the eyes Shemp style.
OK I replayed Oblivion, there.