Yeah agreed, but even then the plot is simple and unoriginal, but well excecuted and comfortable. A few friends of mine saw Avatar without the 3D, and had no idea what the big deal was.
Scoring both films on plot alone, out of 5 I would give Avatar 3, and ROTF half of that. I had no idea that Harry Potter was so comparatively unpopular in America though, I guess because it's not home grown.