Earth's Mightiest Summer Blockbuster
The story was absolutely Marvel in every way. It has enough humor to temper the tense situations, and enough character development to make you care as much about Tony Stark as you do Iron Man. Even the side characters get some emotional depth that I didn't expect. Having Loki as the villain was the perfect choice for the first movie. His ability to draw opposing forces into conflict gave a solid basis for the forming of the Avengers. If the Hulk had been the villain of the movie, it would have seemed really unnecessary for Iron Man or Thor to need any help. The story ended up feeling very "realistic" for the context it's set in. If you haven't seen Captain America or Thor, you may miss some of the references made. It's nothing that will ruin the movie, but there are a few moments where you'll be wondering what the heck that asgardian is going on about.
I don't know how else to say that the acting and direction was excellent. It sounds so obvious to just state it, but it really was just great all around. Everyone played their role well. All the scenes flowed well without seeming rushed and without dragging.
The visuals looked so realistic it's scary. I caught myself feeling bad for New York at one point, and had to remind myself it was only a movie. The sound effects helped augment the visuals more than I usually notice. It's great to hear all the clinks in Iron Man's armor as he's flying and fighting. It's those small details that can easily be overlooked that made so much of this movie great.