Welcome to the jungle, baby
Consider that so many of the roles that Arnold Schwarzenegger takes on are so similar, including Predator, and yet this film is so much better than most of the others. I enjoy watching his movies just because he's such a watch-able guy, even in his bad movies (which are many), but I think the thing that really makes Predator stand out is its simplicity. The movie starts, the guys get dropped in the jungle, lots of blood and carnage flies across the screen, and the movie simply ends. No romance, no complex back story, no soldier struggling with problems in his past or even trauma caused by the horrible things he experiences during the movie. This is one of the things that made First Blood so good. It may turn out to be a movie about a lot of muscle-bound meatheads in the woods, but it doesn't insult the audience or try to apply complexity to a story that can't support it.
Interestingly, the movie features two eventual governors. Jesse Ventura even wrote a book which was released while he was the governor of Minnesota and he used his favorite line in this movie as the title. And the book's actually pretty interesting; there are some funny stories in it about things that went on while they were filming this movie. Arnold, on the other hand, is actually (and thankfully) given a relatively small amount of stupid one-liners, which are an idiotic byproduct of hard action movies that I've never really understood the necessity for. They don't reveal anything about the characters who say them, they don't add to the story or further the plot, and with rare exceptions, they're not funny. But I guess comic relief has to come from somewhere, and since complexity is not a requisite for movies like this, I can't really expect a lot of thought being put into the comedic content either.
I watched Predator having never seen it from beginning to end and having just re-watched the original Alien. I am currently in the process of re-watching both series', for obvious reasons. One thing that I notice about both of them is the way they take their time in introducing the enemies which, in both films, are aliens. Predator doesn't waste much time dwelling on the origin of the alien, we pretty much assume it came from a space ship that flashed across the screen at the opening of the movie. Alien, on the other hand, went into remarkable detail about where its alien came from. What Predator does do, very effectively, I think, is that it has the guys fighting some very human enemies, which allows the movie to later take its sweet time in having them realize that the new enemy is not human at all. This is also, incidentally, weakly rehashed in the sequel, using the secrecy of this mission and team as an excuse to have more guys who don't know what's going on.
The death scenes are actually pretty tasteful, given the genre. They are just gory enough to illustrate the violence of the enemy without being gratuitous. Just enough is shown to show how vicious the alien is, and there are some strange things done to and with the bodies that make you wonder about the alien's intentions or needs. The first deaths suggest vengeance if not some sort of ritual, but later ones suggest that the alien may be feeding off of his (or her) victims. Oddly enough, it is not until the awful Predator 2 that we learn that it kills for sport.
Yes, the movie occasionally gets embarrassingly macho, but the skill with which it is put together far overshadows any tough-guy goofiness. Consider, for example, the ease with which the movie switches from showing the guys hunting the alien to their realization that they are the ones being hunted. In some cases, this transition takes place during a single shot and with virtually no movement in the shot at all except a change in someone's expression. It is truly a fight between a group of predators, which we understand because they are human like us, and a single predator whose powers and weaknesses are unknown. It's not Oscar material, needless to say, but it's a great action movie in part because it already knows that.