Vulture or Chameleon, even in tandem, would hardly be a worthy challenge for Spidey. Mysterio and Chameleon, perhaps, since their powers both involve false images. But I heard it was supposed to be Kraven (not necessarily Keaton in that role, though) and that just made no sense since anybody not endowed with Super Soldier serum has to be so watered-down that it's pointless for them to even challenge someone with actual powers (look at Batroc trying to mess with Cap in TWS.) I really, REALLY don't want to see a third Green Goblin (well, fourth technically if you count both Norman and Harry in the Raimi movies). Or should I say, I don't want to see the Goblin done in the third attempt at the franchise. Scorpion, in my opinion, would be the most worthy foe, similar origin for the powers, natural predator of the spider, but with enough to set him apart (no spider-sense, no webs, and a stinging/blasting/acid-shooting/whatever-doing tail). Maybe even throw in a Spider-Slayer or two.
BTW, how long has Amber Heard been cast as Mera, wife of Aquaman? Did I miss something? You'd think I'd have seen that on imdb sooner. Also, apparently former Green Goblin/Norman Osborn, Willem Dafoe, is also joining the Justice League, as a good guy (but which one? Surely not Shazam...) Oh, and Karl Urban is rumored to be playing Ocean Master/Orm in the Aquaman movie.