So.
The first thought I had when it finished was that it was a really engaging and fun (and flat out gorgeous, easily the most visually accomplished animated movie Pixar [and thus, pretty much anyone] has ever made) movie. Probably not as solid as 2, but better than 1 due to sheer scope and ambition.
But now that the trilogy is over, it's clear that Toy Story is a series of incredibly well done movies. But stuff like Wall-E, Ratalouie, Up; those are Pixar's films, and Toy Story 3 just isn't on that level.
It sounds like the most pretentious thing in the world to make that delineation, but it's the only way I can think of to explain the difference.
Day & Night was brilliant, by the way.
As far as the 3D goes, it was kind of just there. It didn't distract but it didn't really enhance either. It just was. I'm pretty sure any digital showing is in 3D so I'll probably just deal with it but if I can find a digital 2D showing, I'd certainly go with that. But if there is none, there's no way you can see this movie on film. The lighting and detail are literally unprecedented in CG animation. Every single thing that Pixar has accomplished over however many years; fur, hair, lighting, cinematography, EVERYTHING; is turned up to like 14 in this movie. Its visual accomplishment can not be overstated. In movies like Wall-E, you're impressed afterward that you kind of forget it was an animated movie. In Toy Story 3 there are dozens of moments that are almost photo real and yet completely fucking impossible. It's an effect I've never seen on screen and leads to a movie that just explodes detail and color and just plain awesomeness.
I remember a conversation in the LTTP Cloudy thread about how Pixar is more restrained, animation-wise than something like that movie which was way more WB inspired in style. That's all out the window here. Woody and Buzz especially each have tons of moments of near-jawdropping tomfoolery. You could slow it down frame by frame and just marvel at all the cool and hilarious detail some dude in Emeryville slaved over for two-and-a-half years.
As a visual accomplishment, it is the most impressive movie ever made, bar none.
As a story, in the library of Pixar's previous works, it's less successful. But by all means, do not let that stop you.