I've had my buddy's Avatar (Pro) in a temp trade for several months, and he decided to sell it. I've been enjoying it even more than Tron, so I decided to buy it. I like almost everything about Avatar - it's very similar to IM in gameplay, but with a totally different layout. LOVE the music and audio. The only change I'd make is to have a 5-second ball save after hitting the Ampsuit target. It seems awfully prone to a center drain after a solid hit. I kinda wish it had been implemented as a captive ball, like Eywa.
I'm planning to replace the Jake-in-a-box with Jake in his wheelchair, with his Avatar standing behind him. This was one of the better movie subplots: an ex-marine gets his legs back (sort of). I'd love to put a Leonopteryx on the playfield, but I think it's too big. The banshee looks pretty sweet swooping down over the ramp, but it's not as colorful.
Avatar is one of Stern's hidden gems. Just like Congo, I think it will be more sought after in 10 years. Ball times are short, but I've come very close to Final Battle several times. I find it just as addictive to play as IM, but without the hefty price tag.