Actually, I didn't like TS2 either. It wasn't horrible by a long shot and it did have a few things on the first one (a more complicated villain, for one, better defined characters for another), but on the whole, I just didn't like it that much. Now, number three I really think is the best of the series. It really hit my sweet spot for movies in a way that hasn't been hit for a long time. It had that sense of greatness and vision that older animated features had, but that I haven't seen in any animated movie other than Miyazaki for a long time (excluding Ponyo, of course).
Edit: Am I seriously the only one who didn't cry at the ending? Not that the ending wasn't genuinely heart-warming and I didn't really like it, but seriously, I can't be the only one who was dry-eyed at it.