I'm imagining it in my head right now not as a fan but as a moviegoer, and it's not awesome at all. I'm seeing an old man robbing a bank with papier-mâché wings, huffing and wheezing because he can't keep up with Peter. While some people will jump and say "it's the harness-!" I'm thinking realistically of what the average moviegoer will think.
Some people seem to think that every Spider-Man villain works for a feature film, and that SM3 could just include any villain. Some can't, and the movie can't. In this case the Vulture makes no sense- neither does the Sandman, for that case. The only reason I can think of them being here is that Sam has an affinity for the classics...not that I have an issue, just that I'm completely befuddled as to why he's so adamant in only having the classics shine in screen debuts (no, Venom doesn't count- if the Sandman were modern he'd be getting the same amount of attention).
Just because a character is classic or known by the fanbase doesn't automatically mean they will ever have the appeal to hold up a film. Case in point- no one I'm familiar with is going to see this film for Flint's behalf. Characters like Mysterio would drag down a film just in the attempt to adapt them, much less make them appeal to the huge audience the Spider-Man film franchise attracts. Just because smoke and mirrors and harnesses work in the comics doesn't mean it would look good on film. Unless Campbell makes a quick cameo they don't rise above anything but filler material for the notables.
And this is why I fear Spider-Man 4's inevitable production announcement- at some point, Raimi actually thought the Vulture deserved to be in what could possibly be the last Spider-Man film he directs...and maintained the belief that Marko has something to offer.