While I think Iron Man 2 and Age of Ultron are among the weaker entries in the whole shebang, I didn't really think about why, other than that the main stories were not particularly engrossing or well-written in general. One might argue that it's because their ability to stand alone as good movies was compromised by all the set-up elements that were shoved in, but I hadn't really thought about them in those terms. Mostly, I thought both Whiplash and Justin Hammer were pretty lame bad guys, and Ultron kinda boring, despite all of his amazing abilities. I usually like Sam Rockwell in pretty much anything, but he was wasted in Iron Man 2, and I've never understood why anyone likes Mickey Rourke. I didn't know that Ultron was voiced by James Spader the first time I saw it, but thought he was boring as hell, and when I found out Spader did the voice, I understood why because I think Spader is boring, too.