These prequels could have been managed in two good movies, as had originally been planned. I know it could have been accomplished as such, because -- as it stands -- we got one great movie, one pretty good, and one awful. With some much-needed condensing and finessing in the latter half of the second film, a third would have never been "necessary."
Not to keep this thread off topic, but, as a big LoTR fan, it's hard to resist. I totally agree with everything you said. I thought An Unexpected Journey was great. There was so much criticism of the movie when it came out about it having too much dwarves messing around, singing, etc. in Bilbo's house, but I loved all those scenes. It felt like the LoTR movies, where it slows things down at the right times so you can get to know the characters. That's why the LoTR movies were so successful, because they made you genuinely care about every member of the fellowship, and even side characters like Eomer, Eowyn, Theoden (Rohan is just awesome in general), Elrond, Galadriel, and Faramir. Coming into the first Hobbit movie, I was concerned that it wouldn't make me care about all these dwarves, but by the end I was totally on board with them trying to get their home back. The riddle game with Bilbo and Gollum was also so well done.
The second movie was still enjoyable, but you could definitely feel the padding beginning to show with all the Thranduil, Legolas, Turiel stuff, and some of the hijinks with the weasley guy in Laketown, which were not even funny really. I did like the stuff with the necromancer, though, even if isn't totally supported by the Hobbit book, because the White Council did confront the necromancer in the lore at Dol Guldur, and it is a nice tie in to LoTR.
Then the third movie was just a mess of action set pieces. I still cared about Bilbo and Thorin, but the stakes didn't feel all that real, and the CGI battle was nothing compared to battles in LoTR like Helm's Deep and the Battle of the Pelennor Fields. It's too bad because every year or two I do a re-watch of the LoTR movies, and I would love to include the Hobbit movies in that those re-watches. However, I just can't really justify spending the time watching them because it's so hard to get past all the little things (and some big) that they do wrong.