Great special effects, decent acting, and good direction go hand-in-hand with an interesting story-line.
Of course, parts of the story remain silly, and some of the interesting plot points are left in the air, but as far as monster movies go, this is one of the best.
The action scenes are ably executed, as is the suspense and growing feeling of paranoia.
The mystery and the thrill of its premise, of course, is not knowing what is part of this dangerous "game" and what is reality, and just where the conspiracy ends.
The film is an exciting roller-coaster ride full of sci-fi clichs with a smart script that manages to make them all seem fresh and funny.
Of course, many other episodic elements are included: there's melodrama, action, adventure, silly heroics, lots of special effects, and a whole lot of FUN (did I say that already? The cast is just perfect and Allen, Weaver and Rickman have never been funnier.