Spiderman certainly could have continued. I don't think the origin can be as good as the first film and we already had Doctor Connors in the last two films so the lizard tale could have continued. I guess not having Toby McGuire and Sam Rami available made the execs decide to start over. Spiderman 3 could have been good if they only had one villain (probably only the Sandman). The Venom character ruined the film. We were left with Peter and Mary Jane in an uncertain relationship (they did get married in the comics) and we still had Gwen Stacy and Betty Brant available for possible romantic interests. I would have preferred them continuing the original series.