Roger Ebert says it "it works gloriously as space opera." SFSite says, "I found Zathura an absolute delight."
The BBC reviewer likes it:
Though some of the intergalactic mayhem may be too intense for very young viewers, this exciting frolic is perfect family fodder with a pleasingly retro feel and a sly wit that ensures grown-ups will be as entertained as their children.
Entertainment Weekly likes it, too:
From a Hollywood that often settles for less in the family department, Zathura is a rarity: a stellar fantasy that faces down childhood anxieties with feet-on-the-ground maturity.
But some folks had some of the same problems we did. FilmCritic.com says,
And what a boring game it turns out to be once it actually gets started! Zathura spends a ridiculous amount of time at the beginning to establish the fact that the boys hate each other. For nearly 30 minutes, we're subject to non-stop, obnoxious yelling and screaming between Danny and Walter.
The NYTimes review is here.
This film, like Jumanji before it, is based on a book by Chris Van Allsburg.