What I liked:
I liked the tripping out on the government agents.
I liked the sudden animation and the neat trick that Olivia had in her home. I thought it was the actual Olivia and not the small kid.
I liked the sudden change of animation to real person to animation once again.
I liked animated Leonard Nimoy.
I also liked how Bell finally went away and the cost of it to poor Walter.
What I didn't like:
I guess the whole going into someone else's mind is old hat thanks to Inception. It is also rather difficult to determine what is real now given the sudden changes in the plot. That's my only complaint. It hasn't gotten to the level of Lost though.