What I've heard anecdotally:
- Raimi shot all or part of Evil Dead as a film school project, super low budget. Bruce Campbell was his buddy from college, and that was his first "official" acting role
- Obviously, the first one was a straight horror film, but super low budget / relatively poor quality due to the above
- Raimi got the idea to remake the movie frame-by-frame, but making it a pseudo-comedy / horror movie instead, so they remade the movie -- which is Evil Dead 2, which basically "replaces" the first movie
- Evil Dead 2 was also low budget, but is a cult classic because of the innovative horror / comedy approach, and also because it highlighted Bruce Campbell's unique acting style -- catapulting him to C-list stardom
- The sequels were pretty lame, but the Starz series based upon Evil Dead from a few years ago went three seasons, and was pretty entertaining
Of course, some of the above could be wrong, but that's what I know about the franchise.