Pixar is now, what, 11 for 11?
As a sequel, TS3 does suffer from replaying various bits of shtik that you've seen before. But the whole framing story works well, and the last scene is a bit of a tear jerker. There are also several laugh out loud moments in which I think the whole audience was laughing at once. No mean feat, that.
I saw the film in 3D. I can honestly say that I did not see one case where 3D was used obtrusively, as a gimmick, an effect you were supposed to notice. Neither was the film flat. I think the filmmakers hit an effective balance. (The same cannot be said for Avatar, for example.)
Totoro as Miyazaki homage
"Night and Day", the short before the main film, was not as strong as previous films. I know, I'm reaching.