I'd really like to know... Man of Steel was just an out and out bad film that not only had objective pacing issues and hamfisted writing, but betrayed the character so badly that I can't even say it was Superman.
Iron Man... eh, big fun popcorn flick. Star Trek has an intellectual aura about it thanks to the series and then will never truly be as huge as a movie that, might be well written, but is all about the popcorn experience.
Still doesn't refute the simple nature that Star Trek is the better film of the three. Which is a bit surprising to me since I came into the year thinking MoS would be spectacular and Star Trek a big "meh". Exact opposite... well, no meh for MoS more like a "WTF is this steaming pile!"