Although it's perfectly good to watch, I could do without the Necromancer/Dol Guldur stuff. It detracts from the main story and only really serves to delight fans of the other trilogy, which seems a mad choice IMO. I'd have rather they'd had Gandalf with them the whole time I think, if having him missing for long tracts without explanation was deemed unacceptable.
Ditto the bookends with Ian Holm. I love him, of course, but he's of no use here. I'd also take a machete to the scenes in Bag End: what's so comical about that chapter in the book is how much happens in an incredibly short space of time. We have to feel that Bilbo's been given a fleeting window into a different life, then it's snatched away again, in order to believe he'd truly want the adventure. Instead, that stuff goes on forever and the dwarves are only an irritation, to us as well as to him. By making that part so long, they took away both the comedy and, to me, the essence of the scene. We're relieved when they're gone.
There are other things I'd cut, or potentially add (from the extended editions), but that's the most significant.
