A lot of folks on here have claimed there was a Marvel/DC competition out there.
But, I've always thought people just felt too burned out from DC after a long string of bombs, misfires and lackadaisical attempts at their favorite characters since 1997. Christopher Nolan's Batman got away from the herd because it was operating in it's own universe. Smallville stayed on for so long, due to charity from the cast (taking over producer credits, etc).
I figure people just didn't want to like it from get go and was looking for any reason to hate it before giving it a chance. Marvel has taken off since 2008, establishing continuity in it's funnybook universe and I assumed a lot of people were just comfortable with that.
Man of Steel comes along, as the first piece of Time Warner's strategy of being DC's Iron Man multiple franchise starter, and comic fans didn't want to be forced to collect something that had burned them so recently (Superman Returns).
My complaints were trivial. Too many advertisements, too much effects, noisy ending, Costner/Crowe miscast (should have picked unknowns).