So are we talking about the original Avengers appearing? There's going to be Ironman, Thor, Captain America and who else? Wikipedia said the other originals were: Wasp, Ant-Man, and Hulk (I see him better as a villain). Hate the Wasp and Pym. I like Quicksilver and the Vision but not Scarlet Witch. Doctor Strange would be cool (with Gary Oldman as Strange)!!
Who's the villain? Hulk? Hulk being manipulated by one of the archenemies of the above Avengers? Red Skull, Loki, Mandarin? The Leader? Who would you like to see as the villain?
