I've been a Tolkien nerd for years. Read all the books, seen the movies, played the games. So when a friend offered to let me borrow the extended edition of The Hobbit movies, I took the opportunity, even though I'd already seen the theatrical releases and knew the series was flawed.
Lord of the Rings movie trilogy was a masterpiece by Peter Jackson. There were a few warts, but overall it's one of the best adaptations of a Tolkien story that has ever been created. When he took the helm on The Hobbit films, expectations were for a similar result. Perhaps that was too much to expect, because The Hobbit isn't in the same class at all. (Jackson himself knows the whole production was flawed.)
The Hobbit films are just under 9 hours long in the extended editions, and just under 8 hours long in the theatrical releases. Unfortunately, there's only about 4-5 good hours. The rest is extraneous extended action scenes, a ludicrously awkward love plot, and blowing minor characters all out of proportion.
The films are pretty good when they're telling the core story from the books. The initial unexpected party at Bag End, the trip across the mountains, the riddle game, dangers in the forest, Bilbo's verbal fencing with Smaug, Thorin's struggles with corruption...all that is good stuff. I also thought the added component of the White Council fighting to drive out the Necromancer from Dol Guldur fit well, even though it's barely mentioned in The Hobbit book and not described in any detail elsewhere. It worked in the films to establish the big picture and tie into the Lord of the Rings series.
If that's all there was to these movies, they'd be great. But there's several more hours that just do not fit well at all. Many of the action scenes should be about a third of the length (i.e. the escape from Goblin-town) and several are completely unnecessary (i.e. pretty much everything with Legolas). The Elf-Dwarf romance was awful, both in story and cinematic terms. I personally don't think any romantic component was needed at all, but if it had to be there, I can think of any number of better ways to do it. The entire Lake-town portion should have only taken about five minutes: Alfrid didn't need to exist, and too much time was spent to emphasize the Master's greed and incompetence. Smaug didn't need to spend forever chasing dwarves around the mountain before heading off to Lake-town. The battle of the Five Armies could have taken about one-third of the time and still been epic. (Though don't cut out Dain on his battle-boar and the dwarf ram cavalry - they were amazing.) And so on.
If The Hobbit series had been told as two films, without most of the non-book components, I'd have loved it. As it is, I'm glad I watched it once (well, twice, if you count both theatrical and extended versions) for the good parts. But unlike the Lord of the Rings trilogy, I doubt I'll ever spend the time to watch it again.