I went and saw it last night and really enjoyed it. Daniel Craig and Harrison Ford were so much fun as Cowboys.
The only thing I wished they would have explained more is WHY the aliens wanted the gold. "It's rare to them" was kind of lame.
By that point I'd kind of given up trying to figure out "why" it was all going on and was just enjoying it. If they'd said the aliens were harvesting cactus, I'd have been like "ok- let's kill 'em all anyway."