These were my thoughts when I first saw Iron Man 2:
While watching the beginning of the second film, actually I might say up to about 45 min or something, I thought it was a bit flat. I thought that this could be because for a lot of these hero-style films, the first film is usually more interesting as the main character discovers their super-powers. Mmmm. I was about to back up that statement with examples, but could only come up with Spider-man really. X-2 better than X-men, Superman 2, Hellboy II!
Anyway, I thought the first 45 min were a bit aimless, until Sam L Jackson showed up and told Tony to stop arse-ing about. At that point the film developed some plot and became a whole lot more enjoyable, though I was confused with why they replaced Terrence Howard with Don Cheadle as Rhodey. Jon Favreau has done a great job with these two films, including a massive cameo for himself (actually I think it goes beyond a cameo).
Though it is undoubtedly the weakest Iron Man film, seeing it again over four years later with far more MCU movie experience under my utility belt, I found more to interest me. Perhaps, initially I had been a little bit dismissive of it.