Took the family to see this a week or so ago, after liking the first one, and hearing all the buzz. My first impression was that it was pretty much fun, and we'll probably pick up a copy on DVD when the time comes, as the kids really enjoyed it as well.
As previously mentioned, I love animation, and CGI in particular, and S2 was no letdown on that front, either. Granted, I'll notice more when I have the chance to watch it a few dozen times, but the opening sequence, with the horse riding across various terrains, was really awesome, and the rest of the movie was fun to watch as well.
Having said all that, it was a bit disappointing that they chose to tackle the same "don't judge a book by its cover" issues that the first movie dealt with, and not as enjoyable that part of the tension that the movie built up was between Shrek and Fiona; in my mind, I would have preferred to have the problems arise from outside the two of them, and not have marital difficulties play such a big part.
But hey, it's all just a movie, right? And again, a fun one at that, and worth adding to the collection, probably.