It's an unnecessary sequel, sure, but Pixar still tried their hardest to make it as good as they could. And they succeeded, for the most part. I wouldn't call it the best in the series tho.
The first half is rather cheesy, but it ultimately delves into one of the craziest second halves of a movie I've experienced.
This was... something that happened. The atmosphere certainly succeeded in disturbing me throughout the whole thing. Despite a slow pace, this leaves a mark on you. Could become even better in retrospect.
★★★½ Added 1
This was something else. Jim Carrey's pretty good in it.