Not great. Definitely a product of its time.
It's pretty much an artless movie to make a quick buck on Halloween's back where nobody really seemed to care. This is pretty much confirmed by the producer.
The special effects are pretty good, and it accidentally manages to create a good mythos with the camp grounds setting and Jason's vengeful mother killing for her lost son. Some kind of "reverse-Psycho" inspiration was in there, I'm pretty sure.
And if you don't think too much about how nobody's found Jason in the woods in about 20 years, including the police and his distraught, loving mother who would have done everything for him, the idea that he didn't actually drown and starts killing himself to avenge his mom is a pretty good idea that made for a MUCH better movie in part 2.
I actually feel that one of the things the Friday remake got right was that Pam Voorhees first rampage is also her last, and Jason witnesses her death as a child. By all accounts, Jason was a sweet and innocent boy until the sight of his mother's decapitated head drove him mad. It makes more sense having him go missing for a couple of days after his presumed drowning, then coming back to his mom just as she's getting killed, driving him to madness and reclusion at a young age.
Anyway, two of Friday the 13th's main characteristics were terrible continuity and false advertising. The time frames between movies rarely make any sense, very few of them take place on the titular date and they had subtitles that indicated it would be the last move in the series twice, and both times were lies.
