TIME FOR THE FIRST SERIOUS REPLY IN THIS THREAD.
I watched the series as it was coming out before it got to be super popular. I managed to finish all of season 1 and most of season 2 but after that I lacked a TV and wasn't obsessed enough to try and download it or anything.
I and my parents went to go see the movie. My parents have no knowledge of Avatar at all. My mom liked it and cried at the the fish/gods scene. My dad thought it was okay, and seemed interested in taking up the series.
My personal opinion of the movie is "It's not terrible." I've seen far worse, and I had little expectation of Avatar from the start. After the initial "OMG THEY'RE ONLY CASTING WHITE PEOPLE!!" I decided to not follow any avatar news at all. So I was fairly level-headed in not expecting too much or too little in that regard, I think.
The 3D in Avatar was stupid. It's a sad, sad day when the movie previews pop out more than your damn movie does. A friend of mine told me the day before that Avatar was not meant to be 3d and they added it last minute to make more money. I should've took his advice and not seen it in 3d, because it was basically false advertising. I figured that since the bending was cg, at least that would be 3d. It wasn't. Sigh.
The butchering of the names wasn't too bad either, I just kind of wish the picked one way to say things and stuck with it. Katara starts out saying Aaahvatar but by the end of the movie she says it normally. Other characters have different pronunciations as well. I guess I could chalk it up to "accents" but that's giving them too much credit.
I could tell the movie was trying to be funny, but ultimately the humor failed for me. "Don't do water bending near me, I always get wet" was shallow and when it happened in the middle of the movie it was like.... "Wtf, that was pointless and not funny at all." But maybe I'm strange because my parents laughed at it. :/
The whole movie just seemed like a rushed prologue and I was wondering when the "real" story would start.
tl;dr I think the movie would've fared better if it was simply based on the series rather than a translation.