This was one of the more interesting movies we had seen in maybe 10 years. I thought the imaginary plants were nicely designed. Our son watched a second time in 3D, the next week, and it seems the 2D was easier to watch, for him.
i just saw it last night. the plants were rad; i would totally live in that jungle! the plot was pretty cliche, though. the movie started off original and intelligent but it ended up falling into a stereotypical plot. it also went on for way too long and ended up getting far-fetched near the end; jack sully gradually morphed into a super-hero who could do anything. but yeah, the alien jungle made up for all other shortcomings. pretty creative!
The big tree was nifty looking. If an Avatar 2 is produced, they could start the movie at the location of the fallen giant. In which case they would need to consult with a mycologist.