Ironman was hands down the best super hero movie I've seen to date. Robert Downey Jr. was born to play Tony Starks. I read the comic books and didn't know how it was going to end so I'm not sure why you would walk out so early. There were several ways it could have went early in the movie.
Being a fan of comic books, I also loved all the innuendo in the movie like when Col. Rhodes looked at the Mark II suit and said, "Not just yet" indicating that he is going to eventually become War Machine. Also, in the background in one of the scenes you can see where Starks is working on Captain America's shield.
On a side note, I loved the preview for The Dark Knight and during the trailer someone says, "I want to introduce you to someone, Mr. Clark Kent" and the scene ended. If you watched I Am Legend, in one of the scenes they showed this image:
Marvel and DC are going all out with integrating all of their heroes into many, many movies and I have a raging boner just thinking about it!