If it is December, it is the Abyss, and if it is the Abyss, it is a good time for anyone who enjoys beer.
The Abyss is, of course, the annual reserve from Deschutes, an imperial stout generally considered one of the finest you can find. How does the '11 stack up against previous years? Very well. In fact, this could potentially be the best release yet. I say potentially as the "best after..." date is about a year from now.
During a vertical tasting of the '10 and '11 at Hill's -- run down there and they might still have some left -- the '11, for me, came out on top flavor wise. They're both very similar, of course, but the molasses is a bit more pronounced this time around as are the hints of bourbon. The '10 is a lot smoother with a thicker mouthfeel, largely because of the aging.
As it stands, as of December 2011, I'd say they're both awesome, and which one you'd prefer would come down to your personal preference on raw flavor VS mouthfeel. I somehow doubt you'd really notice too much of a difference if you drank the two a couple of hours apart.
Either way, you should pick up a couple of the '11 for cellaring. It's well worth it. Then run out and drink one on tap. Hill's might still have it, and we know both Jones Radiator and Saranac had it last night.
The Abyss is one of a kind (or maybe more like two or three of a kind, but you know what I mean), one you can quietly sip and enjoy like the top-of-the-line libation it is.