This is not a great movie. It's definitely a B movie. It was clearly done on a low budget, belongs to a generally unremarkable genre, and has a plot that leaves much to be desired. For all that, it's actually not nearly as bad as would be expected.
The major premise (that in space there is some kind of immateriel life form that possesses human flesh and wants to kill people) is obscurely bogus, yes, but many much better movies are open to the same criticism. SpiderMan's premise is hardly more realistic, for example, but that is a major motion picture and gets very good reviews.
Then there's the plot. Sure, it's a little thin, but the movie does *have* a discernible plot (not something you can take for granted in a B-grade movie), and what is more, the plot is quite coherent. You do not find yourself confused part-way through about what is going on, which of the people on the screen are from which group (good guys, bad guys, et cetera), or any of the other vagaries that often haunt the plots of lousy movies. The plot isn't deep, but as far as it goes it is solid.
The acting, moreover, is not bad. I did not notice a single instance of noticeably poor acting. Not that anyone's going to win any awards for the acting in this movie, but they don't do anything to break all pretenses of mimesis and make you want to scream at the actors, either. This is fairly unusual, especially for such an obviously low-budget flick, and extra-especially in the horror genre. You expect, in a movie of this sort, to be disgusted when actors stutter, scream at the wrong times, leave long pauses between lines, and have wooden, unlifelike expressions on their faces. I didn't notice any of that, unless you count characters who were at the time possessed by the alien life form, and that was clearly a deliberate charactarization of the menace as quirkily unhuman.
As for the writing, I've seen worse. The characters were mostly flat and static, but horror movies seldom make any pretenses about having round, dynamic characters. Only a couple of the characters were really obvious stereotypes (notably, the scientists' boss and the deputy).
Probably the worst thing about this movie is that the ending quite obviously left things wide open for a sequel.
