Better than average for what it does.
Toy Story 3 is pretty fun to play overall, especially on the split-screen co-op option. It makes it easy to tackle missions with teamwork. You can tell that this game had a good development period as it shows in the level of polish and the lack of bugs in general. It even borders on being a game that I'd pick up and play without my son having to be there. That, in and of itself, makes it easy for me to review this game as "better than average."
If you're looking for a game to play along with a child, this is the one.