It has good CGI special effects, and, unlike many other movies, it doesn't wallow in them. It was refreshing to see fairly long stretches of real humans moving the plot along by interacting with each other. At one point, I started to get bored, but overall it was an entertaining film. It has fun action, sympathetic characters and some funny bits that made me laugh out loud.
Also, Robert Downey Jr. was well cast as Tony Stark. He had an aura of a sort of world weariness with an edge that gave his character an air of authenticity. It's worth seeing the movie just to see him in it.
And, if you are a true fan, stay through the credits. There is a bit of lagniappe at the end.