I don't think Iron Man 2 is bad, I think it suffers in opinion because it is (IMO) the first movie to fit the MCU mold, which makes it tonally different from its well regarded predecessor. Iron Man was largely a stand alone superhero tale, being the first MCU movie. IM2, on the other hand, begins bringing in the larger Marvel universe in Nick Fury and Black Widow. I feel like it has more Feige influence in its DNA, whereas IM1 has more Favreau. If you view it through that lens, as more of the first real MCU movie instead of as a sequel to Iron Man, I found for me it was way more enjoyable.