Good physics, well designed controls and awesome fun factor. Weather effects + deep powder on wide open surface = great.
The controls definitely have a learning curve IMO. Took me probably an hour. Thankfully they give you a "quick reference" sheet for all the button combos when you are doing challenges (i.e. right stick forward with LT pulled for a specific grab). Cannot live without that. I haven't used the in-game trick manual.
The physics are good overall. There seems to be a few glitches with rails/trees and grinding surfaces, but not enough to turn you away. And if you do fall due to glitch, it will restart you and you can hit it again without having to do the entire run over to hit the particular spot.
The dynamic weather is the best feature of this game. I have hit a few spots early when I started playing where I was taking big air and then crashing into a rock face cliff -- not good. In a few spots I had to find an alternate route because there is no way I could clear all the rock. However, come back a snow storm or two later and its covered, and now you can hit it.
I have only been on the first mountain so far (about 4-5 hrs playing) and it is huge. I can't imagine how big the others are.
I have yet to be online. I am not sure the online community will be too big though, being as that I have ranked Top 10 on X-Box Live for scores on more than one occasion, and I am really not that good.
I will add more when I play some more. For now, you cannot beat it for $39.99.