I've dumped pretty much all of my free time for the past week into this game (and some that wasn't really free to boot). I have one character around level 45 with capped out sneak and archery, and smiething, while speech and enchanting are getting close. I've finished the main quest, thieves guild quests (having a fence with 3k gold is so nice), and dark brotherhood quests, and pretty much generally gotten a ton of random things completed as I played and explored and talked everyone up. My character is officially awesome now, and I can even manage to down a couple bosses without being found (no can do with stuff like dragons or trolls though, who seem to even scoff at invisibility). And after all of it, there's still so much stuff left to do that it makes my head spin.
As for the game itself, it's too damn good. I seriously can't stop playing it, even if I try. I even can't wait to make and level my next two characters to try out some other things. I'm playing on the PC and there are certainly some bugs. I've only crashed twice in 10 days, but some things are still glitchy. The most notable being quest requirements. For example, I picked up an alto wine for some quest, and now I have around 20 of them in my inventory and can't do anything with any of them (since one is a quest item, I can't use, sell, drop, or store any of them in the stack). Also, if you get a new quest requirement that's already been completed before you got it, it doesn't register as such and there's pretty much no way to ever complete it. So say you need to clear out a cave of bandits, but you already cleared it out randomly 20 levels ago when you ran across it, too bad. But it's all such minor stuff when there's so much else going on that it doesn't ruin my enjoyment of the game at all really, and I'm sure it will get patched. The quest log in general also needs improvement.
With patches and DLC and a devkit and mods all still to come, I've already gotten my money's worth 4 times over and loved every minute of it. I'm so in love with this game that I'll probably tinker with the devkit for myself and see if I can come up with anything cool, though I'm pretty short on ideas beyond the quest log. It's so good that I haven't even gone out to buy Skyward Sword today! Hell, I haven't even beaten the first level of Mario 3D Land, which I also got a day late while I was out anyway, but this week I'm on the road more. My forum time has suffered as well.
GotY? It's certainly got my vote, but it has to contend with Skyward Sword which I haven't played yet and hear is amazing, so I hope I get around to taking it out of the box before 2012. I just haven't been this addicted to a game in years. Even Fallout 3 and Oblivion didn't pull me in like this, and I thought they both deserved GotY as well. But those games didn't have to contend with Skyward Sword, so we'll see.
I highly recommend the PC version of this game over the other two, for the record.