Love the movie.. Hate the game..
The game however, is a complete detraction from the movie. The story is not there, and it is plagued by many design issues along with several bugs, including but not limited to missing options and frequent crashing.
The world is a carefully designed maze of virtual corridors, designed to funnel you along mission guidelines. No "big open world" here, despite what the movie showed us. Mounts aren't always at your disposal - they are only available during certain missions. The HUD, while adequate if not overly simple, can only be displayed by hitting a key - there is no way to force it on permanently. Not to mention, it isn't integrated with the game in any way (like a digital display off your helmet). It is a simple overlay that fades out when it wants to.
I felt absolutely zero sense of connection to my character or his avatar, and the same can be said of all NPCs for that matter. Run n' Gun seems to be the overriding style of gameplay for Avatar, which is truly sad for what could have been an engaging and deep game. My first hour of play was spent running/driving around shooting any and all planetary lifeforms, or bashing them with my vehicle in the pursuit of a nav point where my mission sent me.
Lacking any emotional involvement, depth of story, and adequate HUD and interface design control, leaves the game without much to stand on.
Don't buy this one - if you need an Avatar "fix", go see the movie in 3D again. They completely dropped the ball with the game.