There are no original stories anymore. Everything, to some degree, has been done before. So in the modern milieu it's not about if your tale is original, rather how you tell it, that counts.
And 'Avatar' is beautifully told.
It's basically 'Dances With Wolves' relocated to an alien world, with Thundercat-like natives and a strong enviromental message.
Sure, the dialogue is ropey in places. Yes, it's an effects-heavy movie and the pacing could be better. But James Cameron is a master film-maker and passion for the world he's created blazes through every single frame of digitally rendered footage.
Both the Blu-Ray and DVD transfers are absolutley stunning. 3D is a dismissable gimmick after all; you'll be pleased to hear that none of the film's sense of wonder is diminished on a half-decent 2D TV screen.
Is 'Avatar' the greatest sci-fi film ever? Of course not. That accolade arguably goes to 'Aliens', an earlier James Cameron movie.
'Avatar' is, however, one of the best sci-fi flicks of the last two decades and it sooooo deserves a place in your DVD / Blu-Ray collection. :-)