I've heard that The Avengers is a very fun popcorn summer blockbuster. There's always a film like that in the summer, that becomes a hit with audiences and critics (Spider-Man 1 & 2, Iron Man 1, The Dark Knight, etc). There are also plenty of blockbusters that get average reviews yet still become hits with audiences; The Amazing Spider-Man comes to mind.
I have a feeling Man Of Steel is going to be a blockbuster that gets shitty reviews but a decent to good reaction among audiences. Similar to the recent GI Joe, POTC2, or Clash of the Titans. The problem is that Man of Steel's budget is pretty big, and the marketing budget is huge. It's going to need legs, and bad reviews could fuck that.