Carnage: Hell no. Enough with the idiot era of Marvel Comics.
What's wrong with Carnage?
The Rhino: Has potential--if used as orignally created, and not written off as a dumbass. He needs to be a brutal killer on screen--not suggested through the Daily Bugle, or bystanders.
Rhino has always been something of a dumbass to create a fair balance. You can't be too smart if you've got such enhanced strength and speed. Maybe if part of any potential plot took elemants from Flowers for Rhino, then maybe you've got the premise for him being so dangerous as for Spider-Man to be needed to stop him.
As far as your brutal killer stuff goes, I'd say that's perfect for our ole' buddy Carnage who, in the Ultimate universe, must kill for sustenance. Plus his origin is tied in with Connors very well here and is partially established.
Original or not, if it has been penned then it's fair game as far as I'm concerned. The "ultimate" story involving Spidey/Connors/Carnage is perfect.