>but it didn't get much attention when it was first realesed leading to there not being any sequels

Well, the Silence of the Lambs was the sequel to the book Red Dragon, which Manhunter is an adaptation of. Would there have been a stand-alone Silence of the Lambs if Manhunter hadn't been made? I don't know, but usually a film adaptation of the first book in a series is made first; since Manhunter was already made, there was no sense in doing Red Dragon again at that time.

As everybody else said, it is very good, though not quite as true to the source material as the Red Dragon movie years later. I can't say I prefer one over the other, although Manhunter is a very unique film with a peculiar atmosphere, where Red Dragon is very much in the Hopkins-as-Lecter universe.