Personally, I'm not entirely convinced this will work. I want it to - don't get me wrong and I'll be first in line come opening day..
But is it really a 'Monsters' movie without Boo? I mean, she was the one to give the first film humanity, we were scared and worried for Boo through Sully's apathy. I don't think we'll see that this movie.. Just a bunch of gags. Again. I want to be proven wrong and certainly hope I do.
I hope it works, but I do agree Boo was key to the first film working, but if they can come up with something equivalent to the door chase at the finale of the first they might at least have a decent prequel.
But I am getting the feeling we are entering a new phase in Pixar's evolution, and it may take a few years of "ok" films before we hit some more "classics".