One thing about him and Spider-Man, he's have great moments and balance them out with awful moments. "The Night Gwen Stacy Died" was great, but up to that point, he gave Gwen her worst moments as a character. Her one panel in the issue before has her saying "You've got to come back Peter. It's Harry. He's...backflashing." Either Conway really didn't know how to say "He's having a flashback" or "he's relapsing," or he was deliberately trying to make Gwen look stupid. He wasn't the last Spider-Man writer to have contempt for at least one of the characters he was writing about, but he was the first.
Possibly the best thing to come out of those two issues was how they gave Mary Jane some depth and expanded her character, then he ruined it a decade or so later by having Mary Jane always know that Peter Parker was Spider-Man. At least he's not the one who brought Norman Osborne back from the dead.
And he did write the Superman/Spider-Man team up, which had a few nice moments, but was great just because it was Superman. And Spider-Man. Together. In 1976.