Roger Ebert says:

The experience of the movie is joyous. I don’t even want to know about anybody who complains they aren’t hearing “the real Beatles.” Fred Astaire wasn’t Cole Porter, either. These songs are now more than 40 years old, some of them, and are timeless, and hearing these unexpected talents singing them (yes, and Bono, Izzard and Cocker, too) only underlines their astonishing quality.

Stephen Holden says:

Because of its oh-wow aesthetic, its refusal to adopt a critical distance from the ’60s drug culture, its tacit approval of the characters’ antiwar activism and its token attention to the decade’s racial strife, “Across the Universe” leaves itself wide open to derision, complaints and endless nitpicking. But it couldn’t have succeeded any other way. The movie is completely devoid of the protective cynicism that is now a reflexive response to the term “the ’60s.”

And:

I realized that falling in love with a movie is like falling in love with another person. Imperfections, however glaring, become endearing quirks once you’ve tumbled.

This is my new favorite movie. Even Bono couldn’t ruin it. Everybody who doesn’t like it is nuts. It’s rotten at Rotten Tomatoes! Nuts!

Just don’t go in expecting a cultural and political exegesis of the entire 1960s, because that’s not what it’s about. I guess that’s what’s tripping up some of the critics. Others are just, as the man says, protectively cynical nitpickers.