I just saw The Hobbit. If you're going to go all purist on this, stay at home with the book. If you are looking for more fun excitement than a sack full of monkeys, with some fun elaborations this is the thing for you.
Look out for some illumination on one of Tolkein's lesser known back stories re-imagined as a mad cat lady. I always envisaged that character as a mysterious figure, flitting through the woods, so this is a welcome different take. More interest comes in the form of a fleshing out of the Sauron story arc.
The Lady Galadriel shows up in a disconcerting way: it's obvious she has aged since her appearance in LOTR. The only major 'blah' factor was the alteration to the troll scene. If you have read the book, you will spot the change immediately. The production downside is the same old semi-heroic, faux-Celtic soundtrack which makes my sinuses reverberate and my nose want to run. Apparently the recycled soundtrack released budget for other parts of the movie, so I can live with that (slightly).
You can see Jackson reaching for the schmalz sentimentality again, but Martin Freeman manages to avoid all that. His facial expressions deflate the emotional pomp in a very welcome way.
It's looooong, so maybe take a picnic basket and a portaloo. I can imagine the extended edition running to two bowls of home-popped popcorn.