It was terrible in the kindest way said possible. Terrible acting, plot speed and development, and very little loyalty to original storyline arcs.
And wtf! Fire benders can't make fire shoot out their hands by themselves!? BAH!
It's The Last Airbender now, stop associating a perfectly good television show with that crap.
In retrospect the cartoon wasn't totally awesome either, but at least it showed real potential. I think that had more to do with budget and time constraints though.