I feel as if this is a completely erroneous claim, but what you have to know about movie critics is that they all have specific critieria that they judge a film on, and straight up, some people will disregard films because they're not "important". That's kind of what the Academy Awards does these days- critically acclaimed mainstream comedies will get the shaft over something like The Help or The Iron Lady which talk about important social issues & feature acclaimed actors/actresses.
If this is about the Roger Ebert review, you should know first off that A. Ebert loves comic book movies, but hates dumb ones (He's given 4 stars to Batman Begins, The Dark Knight, Iron Man & Watchmen, and highly revers stuff like The Crow, the Hellboy films, the X-Men films except for Wolverine, etc) and B. His tastes line up with the public more often than not. He's known for his "relative, not absolute" criticism, where he sets out to see how a film succeeds on its own merits & for its audience first, then critiques it as a whole. For example, this is a quote from one of his reviews:
When you ask a friend if Hellboy is any good, you're not asking if it's any good compared to Mystic River, you're asking if it's any good compared to The Punisher. And my answer would be, on a scale of one to four, if Superman is four, then Hellboy is three and The Punisher is two.
A lot of reviewers are finally taking this as the basis for their criticism. As they should. Sometimes you have to award the film based on its own merits, not necessarily whether it's what you expected it to be or not.