I dunno, in the prequels I was quite impressed with the CGI. Only a few times did I say to myself "oh man that looks fake." Examples include Anakin "surfing" on top of that bulbuous cow type creature in AOTC, Padme's a little TOO perfect "action figure riding vehicle" posture on top of that animal in AOTC's arena scene, and that pan over of the Clonetrooper helmets at the end of the movie (that screamed "video game cutscene"). It was in that scene that I thought the clones must have been CGI, but I didn't realize they ALL were until I read about it later on the 'net.
The Special Editions weren't too bad, except for Jabba (obviously CG) and the Stormtrooper that was riding the Dewback in ANH (c'mon, he flopped around like a fuzzy plastic doll). The 2004 DVD's brought to light how fake looking the "Rontos" were in ANH (practically with big fuzzy lense flares on them), though I didn't notice it on the big screen.
Also on the big screen (the IMAX EXPERIENCE), the first pan over of Kamino's platform in AOTC looked fake (I could see clipping between the object and the background that wouldn't be there in real life), though I didn't notice this on the DVD or the regular theater.
Those were moments that "took me out of it." Sure, a couple of the close ups of Jar Jar in TPM where Obi-Wan and Qui Gon are first talking to him it seemed like they were looking above him or past him, but that was about it. The rest felt pretty seemless.
I actually think the lightsabers in TPM look better than the ones in AOTC. Compare clips. The ones in TPM look bright and "solid" like we're used to from the better shots from the OT, but suddenly in AOTC they look a little too colorful like they were pasted in with a computer (as SURPRISE! they were, but anyway). That said, the effect looks cool, but when you compare the difference it takes you a bit out of the moment.
The effects added to the SE's weren't bad, but the ones that worked best were the ship effects or scenes added where the whole thing was CG, rather than pasting in some character that wasn't there before (like Jabba). Sure the 2004 Jabba was much improved, but since we all know the puppet so well, he just didn't quite cut it.
Yoda in AOTC took some getting used to, I'll grant that. He moved a little too slowly and carefully at times, that made you think he must be a computer construct and they're taking their time to show off his every bone structure and angle. While you accepted him as "real" after awhile, certain shots make his head look really round and blob-like (ditto for some shots in the ROTS trailers) that he didn't seem to have in the OT or TPM (with the puppets). The puppet in ESB at times looks pretty fake but again you accept him most of the time as some old alien.
We aren't to the point yet where "humans" that are CGI look completely lifelike, but space ships, aliens we've never seen before that don't interact too much with real humans, and robots look pretty convincing these days.
And LOTR has shown how crowd scenes and large "ground battles" can be done convincingly with a mixture of CG and real or completely CG. I think we've come a long way.
I'm not of the mind that replacing puppets and models with CGI is automatically better, but also I agree that we're to the point where CGI isn't automatically "more fake."
Still, for established characters (like Yoda) we're used to seeing them "more real" (like the puppet in TPM) so some of that is lost with the CGI. But it's far easier to have a cgi Yoda jumping around in a saber battle than a puppet and make it convincing, so I give him that.
Momentary lapses in the film like I've described aren't just CG either. Every time I see an obvious "matte box" around a ship or something, that yells to me "hey! you're watching a made up movie!" I can overlook it, it's just a little distracting.