I think that Avatar's contribution was much more than simply that it was in 3D. The level of detail in what was being depicted in things both large and small, including seeds on the wind and tiny creatures barely big enough to see, the illusion that all of these things had ecological relations to each other, and then rendering that in 3D to create an experience that made it feel like you are there in something both otherworldly and real, that was the big achievement. It was scope+medium.
I absolutely agree, which is why I said "the 3D technology alone ...". I can kinda understand people critical of Avatar's plot and characters, even though I disagree with them, but to downplay the achievements of the movie in the SFX department is indicating a personal bias clouding judgement.