This is one of my top-ten favorite movies of all time. It's quite easy to dismiss this film based on its genre (barbarian slash-em-up) and the limited acting ability of the star (Schwarzenegger), but Conan is nothing short of a masterpiece.
Ok, the story is fairly standard, and the principal actors (Schwarzenegger, Sandahl Bergman & Gerry Lopez) are competent but not outstanding. There are a few brief but memorable performances from James Earl Jones and Max von Sydow that help lend weight to the film, but the real stars are Poledouris' score and the cinematography. I have never seen a more beautifully-shot film in my life. The costumes, props and art direction are all top-notch. They could take all of the dialog out of the movie, and just have the music and pictures and it would still be worth watching.
To fully appreciate Conan, though, you have to watch it and then watch another barbarian-type film from any era (Beastmaster, Krull, etc.) and the difference will be stunning.