The reviewer who compared Avatar to a video game clearly doesn't play video games, as they are - for the meantime at least - entirely different mediums. He/she is closer to the mark in describing Avatar as being cartoon-ish, and what, exactly, is wrong with that? Some of today's animated films are simply superb, and the Japanese anime genre has for a long time shown that complex characters and emotions can be portrayed through two-dimensional characters.
Onto Avatar. Actually, I wasn't very impressed with the first half hour or so of the film, as there were some rather banal scenes which left me feeling somewhat patronised. A prime example being when when Jake asks what a video diary is... Duh! It's 2154, Jake; your grandmother would have even known. I think audiences are aware that it was being used as an internal monologue device, without it having to be "explained". But then the film picks up, and despite the all-too-obvious and generic Colonel and the sinister company man, the Na'vi characters have a culture strong enough and believable enough to become sympathetic. The overt message may be somewhat heavy-handed and preachy, but its heart is in the right place, so it's hard to fault too much.
Concluding. Avatar will not be everyone's cup of tea, but I would rather it existed than not. The two and a half hours did not drag, it looks spectacular, and give me Avatar any day over the lies propagated in old westerns, where Native Americans were routinely portrayed as savages needing to be put to rights by John Wayne.