Well, ideally, I would want to create a "halfway in between" version that included some of the extended scenes but not all of them, because there were some additions I liked and some I didn't.
Changes I liked:
[*] The gift-giving scene at Lothlorien should never have been cut, especially considering that it's referred to later even in the theatrical version. (At least, I think it is.)
[*] The added flashback scene with Boromir, Faramir, and Denethor in TTT was excellent; it really established the characters well.
[*] Gandalf's confrontation with the Witch-King also should never have been removed, since the buildup to it is still there, and you're left wondering why Gandalf suddenly loses his staff and looks beat up.
[*] The Houses of Healing scene is one of the trilogy's most beautiful, between Eomer's wailing over his sister and the pretty song that comes after it. It's also very nice to have some closure for the characters of Eowyn and Faramir.
[*] The added scenes of Frodo and Sam making their way through Mordor disguised as Orcs really help; without them, Mordor seems about the size of a parking lot.
[*] In all three movies, the extended battle scenes are much better. I'm not saying that because of the violence, but because they feel more balanced and better paced. Whereas before, it seemed like some characters were doing little and the heroes had a bit too easy a time, in the extended versions, everyone contributes and the battle is not so easy.
[*] Similarly, I loved the little added struggle between Sam and Gollum at Mount Doom-- it helps to answer the questions some had about why Frodo was able to get so far ahead.
[*] There really are a lot of other little scenes that, while they aren't necessary to the story, they are neat to see and I have no problem with them either way.
Changes I didn't like:
[*] The theatrical opening to FOTR with Frodo sitting under the tree was much better than the extended version with Bilbo writing his book. It was more focused (on the movie's actual main character), more interesting, and communicated everything the audience needed to understand about the story; whereas the Bilbo opening gets bogged down in unnecessary details.
[*] Adding the funeral of Theodred destroyed one of the most powerful moments in TTT. After being rescued from Saruman's control by Gandalf, Theoden drives Wormtongue out, then suddenly stops, realizing something is still wrong. "Where is Theodred?" he says. "Where is my son?" Cut to Theodred's tomb. The pain of that Theoden's loss seems very real at that moment-- not only did he lose his son; he didn't even get to bury him. Putting a scene in between Theoden's question and the answer diluted the power of that moment.
[*] The scene of Faramir chatting with Pippin at Minas Tirith is nice, but it similarly screws up a transition from Gandalf asking Faramir "Tell me about Frodo" to Frodo climbing up the stairs of Cirith Ungol. It feels odd having that split up by an extra scene.
[*] I really don't like the additions to the Paths of the Dead scene. The original was paced very well and ended on a dramatic cliffhanger. In the extended version, we get more Gimli comic relief, then Aragorn yelling his line long after the scene seems to be over, and the Dead dumping a bunch of skulls on them for no apparent reason

except to artificially extend the suspense. It worked much better when it was left as a cliffhanger.
[*] I wish the scene of Aragorn using the palantir had been able to save the very confusing "Arwen is dying because her fate is tied to the ring" story, but I'm afraid it only makes it more clear that they were never able to get that idea to come together the way they'd hoped.
[*] There are a few other scenes that I think hurt the pacing more than they're worth, but I have to admit I still enjoy watching them.
Please keep in mind that I am being extremely picky about these movies in this post, and I think that Peter Jackson's trilogy completely surpassed what I ever dreamed could be done in a movie version of The Lord of the Rings. So I am very happy to take even the things I didn't like as much; these movies are terrific, as far as I'm concerned.