This is a very good late-night movie, as most of my favorites tend to be. When you're hardly awake, and your body gives you the option of immediately falling asleep when your head hits the pillow, or to just chill out in front of the tv flipping through the weird stations you don't bother with during the day. I saw this when I was 12, which was actually the most active late-night movie year in my life.
The combination of atmosphere, setting, and the sheer isolation the protagonist faces dealing with his 'affliction'...it's just the perfect formula for a fun horror film. Not to mention it came out right at the peak of incredibly horror SFX before the decline in the mid-90s as the people were discovering they much preferred really bad CGI to the look of actual visceral horror. Can you tell I'm bitter? Yes, I'm bitter.
There is something in the film too, which I think a lot of horror directors today have forgotten about, and even most non-horror directors. I actually felt for the characters, sympathy. There's of course room for the anti-hero in a well-written screenplay, but I don't think it is ever nearly as powerful as caring about what happens to him/her when you're watching a movie. It makes the next terrible moment actually terrible, and in The Fly 2, there are so many little (and a couple of major) moments that legitimately make me sad every time I watch this, and enhance the power of the more gruesome moments.
With that in mind, if you are an animal lover, the kind who can not handle bad things happening to sweet little pets...maybe you should stay away from this movie.