Now before I get flamed, I have never read the "Ultimate Avengers" comic book. I have always been a fan of Iron Man when I was a kid, and this is the only reason I watched this animated feature.
The Ultimate Avengers tells the story of the Avengers. We see the birth of the team of Captain America, Iron Man, Wasp, Giant Man, The Hulk and Black Widow. The team is put together when the earth is attacked by extra-terrestrial beings.
The animation is superb! It is nice to see cartoons get back to the animation I was used to as a kid watching Saturday morning cartoons. The cartoons of today are terrible. This was definitely a plus for this animated film. However, the story did not do too much for me. I was hoping for a lot more of Iron Man, but the film mostly centers around Captain America. Again, I have never read the comic, so I can't tell if this is true to the original story. Also, the film was laughably short. Only 70 minutes. But I guess that is to expect from an animated film.
Overall, a fun time-waster. Fans will definitely love the film. I unfortunately, was never really a fan of most of the heroes in this film, so I guess I just didn't get it.