well i rented this a couple weeks ago and beat it, here are my thoughts...
You start the game and after the intro stuff you eventually get to a mission that make you choose between RDA (humans) and the N'avi. i chose the n'avi cause it's the good side so i beat the game with them. I didn't play the human side cause it would've been like another 10-15 hours
so anyway, it's a 3rd person adventure game and the world of Pandora is yet again the star. i'm serious, it's very detailed and colorful, just like the movie. It's not totally open world like 1 big city like gta, its a bunch of diff cities/areas but they're really big and you can explore etc
you get xp for kills and missions and then upgrade your weapons, armors and skills . The n'avi skills are Eywa stuff like turnin invisible and pounding the ground like a shockwave and running fast, and there's one that is like a wind storm that you call in that kills everything and another you can summon a wolf creature of some sort
so as you level up, these powers upgrade and you get new weapons.
the N'avi weapons aren't like humans...but you have a couple human guns like a lmg, but the n'avi weaps are mostly melee like big staffs, 2x claws, bow (used a lot), crossbow, and so on
there's a lot of collectible items...i didn't really put much effort into getting them cause i rented it.
the game gets repetitive in the second half...you just want it to end but it's still cool. if you like Avatar universe as much as i do, i think you should play it. it also has an in-game encyclopedia that you expand by doing this zooming thing with the camera and it scans it so you can learn more stuff about pandora.
you also ride the Thanatos (black tiger in the movie that's brutally slaughtered at the end) and also the flying banshees but the controls for those are terrible
decent game, rent it or buy for 20 bucks after it flops...7/10