I'm pretty much in agreement with everyone here on the most intrusive changes (Greedo shooting first, Hayden's ghost, Vader's "NOOOO" in ROTJ, Boba Fett's voice change, Jawas on Rondos)

What I liked/didn't mind:

Star Wars

-improved matte lines
-new Sandcrawler shots
-Landspeeder underside
-extended Sandtroopers on Dewbacks scene
-improved cell block perspective
-tractor beams
-Ben's hut
-"Open the blast doors!" being reinstated
-Biggs scene on Yavin IV
-air traffic of Mos Eisley, Falcon take off
-improved Vader lightsaber color when hanger doors are closing
-approach to the Death Star
-Death Star explosion (pretty unnecessary though)
-ugly stand-ins at the ending celebration replaced

Didn't like: (other than the obvious)

-I use to not mind the Jabba scene when I first saw it in '97, but in retrospect, it's pointless, and the CGI Jabba looks awful in all three iterations of the SE.. Would be great as an unaltered deleted scenes via extras, but having it in the film serves no purpose.
-Replacing the wolf aliens in the Cantina.
-The CGI robots, Rontos, and other CG creatures added into Mos Eisley. The Ronto walking directly past the screen when Ben and Luke arrive, as well as the Jawa falling off of one, are grossly out of place, and all around terrible.

The Empire Strikes Back

Liked:

-suitmation Wampa (Not needed, but not completely out of place)
-improved mattes in Snowspeeder cockpits
-Falcon's approach to Cloud City
-Cloud City windows (though I can't recall if I prefer the '97 or '04 versions)

There were other small changes done in '97 that I didn't mind, but I wouldn't say I "liked" them. (Vader's extended landing, and the people of Bespin reacting to Lando's announcement, for example). I still much prefer the straight and to the point "bring my shuttle".

Disliked:

-Boba Fett's voice change. I hate this with every fabric of my being. I understand why it was done, but it takes me out of the movie every time.
-Ian McDiarmid's hologram. Sounds like a good idea on paper, but the execution left a lot to be desired, and the change in dialogue was beyond unnecessary.
-Luke's scream. Like somebody else said, why would he scream if he jumped voluntarily? It's so dumb, and really quite distracting.

Return of the Jedi

Liked:

Actually nothing, really. I didn't mind Oola's extended scene, or the herd of Banthas, though

Disliked:

-New song at Jabba's palace. Not only does it remove most of the practical effect shots that were originally there, it's garish, and completely alters the mood of the scene. The extra shots of Boba Fett were pointless, and the CG Sy looks horrendous. It's a mess.
-CG Sarlacc. Completely unnecessary.
-Darth Vader's "NOOO" inserted into the 2011 version. Absolutely horrendous change, and IMO, one of the worst changes in any version of the SE's.
-Ghost Hayden. Arguably, one of the worst changes made to any of the movies, and on par with being as bad as Greedo shooting first (if not just as bad).
-Replacement of Yub Nub. Yeah, I know it wasn't great to begin with, and I don't mind the new song that much, but it just wasn't necessary.
-Removing Anakin's eyebrows.

I'm lukewarm on the expanded ending celebration. It's just kind of there.