I disagree, his script was strong like Sam Raimi's, but once again it was nothing "astounding", if anything Sam Raimi's Spider-Man was the major force that built what the SUperhero genre is today after the Batman & Robin mess, we had Blade and X-Men previously, sure, and X-Men was a major success, being the 9th highest grossing film of 2000, but Sam Rami's Spider-Man was the film that rocked the "genre" and showed that super hero movies could fun and visually close to it's characters and at the same time break records and be a major blockbuster.
Even as a film i find Sam Raimi's script better, it's just more balanced and dark doesn't mean better, and from the around 90% reviews i doubt critics found Sam Raimi's film weak, or hoped another had done it.
As for Leonardo DiCaprio, he would have done well in the role, but at the same he doesn't bring anything new to the role, Tobey Maguire completelly nailed the "puppy face" and "geek" aspect more similar to the classic Peter Parker, while Garfield completelly nailed the teen aspect, something many don't seem to give him credit for just because it wasn't "their Peter Parker".
From the looks of it DiCaprio would have just been the "geeky" Peter Parker but without the actual looks, since it's freakin Leonardo DiCaprio.