COWBOYS & ALIENS Either aliens levitated somebody outta there, or James Bond has gained a few pounds.

A MAN WAKES UP in the desert. He doesn't know who he is, or how he got there, or why there is a bizarre-looking metal shackle on his wrist. This is a terrific opening to a movie, and on a few occasions, the rest of Cowboys & Aliens lives up to the excitement of these first few minutes. Based on a 2006 graphic novel, its mixture of Western and science fiction is ideal fodder for a summer popcorn flick—especially since nobody seems to like the original comic very much, which allows the filmmakers to do whatever they want without raising fanboy ire.

The amnesiac (Daniel Craig) quickly acquires a gun and a horse—and, delightfully, a dog—and wanders into the nearest town, which is under the thumb of grizzled cattleman Woodrow Dolarhyde (Harrison Ford). Before too long, alien spaceships turn up and shoot fireballs into the ground, then abduct some of the townsfolk with fancy metallic lasso-type things. The stranger's shackle turns out to be some kind of space bracelet, and it starts blasting back at the aliens—which aren't ever called that, but rather, "demons."

Journeyman director Jon Favreau (Iron Man) won't ever be mistaken for a visionary; his tone is maddeningly all over the map here. Sometimes the alien creepiness hits a delicious high, but sappy sentiment smears up other parts of the movie. Favreau isn't really sure how to let the science fiction elements shine—the aliens are yet another dull H.R. Giger iteration, and their base is disappointingly easy to infiltrate—and he certainly doesn't get the Western aspects right, either, with both gunplay and the scenic vistas either murkily depicted or totally washed out. But if Cowboys & Aliens never coheres into the ridiculous spectacle it deserves to be, there are more than a few moments—many of them due to Craig and Ford trading dust-dry quips and tough-guy stares—that give it liftoff.