How do you rank Predator against -
1. other Schwarzenegger films
2. other sci-fi franchises
3. other suspense films (not necessarily sci-fi)
I have to say, Predator is my favorite Schwarzenegger film. It worked for me because Arnold was so clearly the underdog throughout the film. This is the best depiction of an outclassed action hero I can remember ever seeing. (I'm not counting horror films where by definition the protagonist is outclassed - because the protagonist is never an action hero.)
As a sci-fi franchise, I guess it doesn't rank too highly with me. (From this, if you apply some logic, you'll realize I'm not that big of a Scwarzeneger fan in general.) The main reason I rank this movie low in this category is the simple fact that the sci-fi concept is pretty basic. There's no big idea that makes me go, "Whoa."
Meanwhile, as a suspense film, I rank this film highly. The outclassed action hero motif is great for suspense. And the Predator concept is absolutely perfect for suspense. I mean, seriously, super-fast, invisible, ruthless, and lethal? Terrific for suspense.
I'd rank it well behind Conan, Terminator, and even several of Arnold's light-hearted fare.
Like you said, the movie is very basic. I was never really "wowed" by it.
It became a classic because of all those macho actors, a hideous looking villain, and an ok survival/underdog story.