Have you ever noticed that both Tobey Maguire and Andrew Garfield's incarnations each end on a downer note?

https://www.youtube.com/watch?v=EWJ5OLa7y70

https://tvtropes.org/pmwiki/pmwiki.php/Film/SpiderMan3

Leans more towards the positive side: Harry is dead but made amends with Peter, and Peter has to come to terms with having acted like a colossal jerk, but he's managed to overcome his dark side, forgiven the man who (accidentally) killed his uncle, and it's implied that his rocky relationship with Mary Jane will heal, and they'll be back together again.

https://screenrant.com/spider-man-3-actually-good-underrated/

Speaking of continuing a legacy, Raimi clearly had plans for the fourth film (and beyond). Spider-Man 3 laid these in place without just becoming a filler film. There was enough of a story to stand on its own and we weren't left with a cliffhanger ending. Quite the opposite, we had the bittersweet ending of Peter and MJ reconciling, and there was still as much room to carry on as there was to leave the story there.

https://forums.superherohype.com/threads/why-is-spider-man-3-so-depressing.373067/