Oh, this is one strange movie. The tag line sums it up well: "Nice planet, we'll take it".
The acting lineup is amazing: Jack Nicholson, Glenn Close, Pierce Brosnan, Annette Bening, Danny de Vito, Tom Jones (as himself), Michael J Fox, etc. It is, on the other hand, one of those utterly daft comedies that defies even the discussion of whether your belief in the laws of physics needs to be suspended.
I can only speculate that it is deliberately aimed at being a "cult" sleeper. It has a (very) few nice touches, such as Martians (crafted with tongue in cheek by Industrial Light And Magic) whose brains explode in response to country music, leaving green jelly.
Hard to rate, perhaps 6/10, but it will not, in my opinion, ever become a cult winner. That is not to say it is not interesting, just that it is not spectacular, in either the commercial or the underground fashion.