(What I'm saying seems kinda obvious to me, but I'll spoiler it anyways because, hey, why not?)
If Gwen Stacy dies in 2 instead of 3 (which seems like the most logical conclusion after seeing that; what else would they need mourners for?), I'm going to be so disappointed. One of the toughest parts of ASM was how much they squeezed into there, including the deaths of Uncle Ben, Captain Stacy, and technically Richard Parker. Rushing the classic Gwen death into this one just feels rushed, like they're trying to squeeze most of Spidey's history into one trilogy.
Only way I see this brisk a pace working is if 3 has an epic battle with the Green Goblin ending in Peter's death a la Ultimate, and I just don't see them pulling that trigger.
This is why I was personally hoping for four films. I feel like it gives the franchise room to breathe even if some may feel the story ends up feeling stretched by the end. Last I heard, they were planning on still doing that Venom movie as setup for a villainous role in one of the Spider-Man flicks. It could make for a decent final outing wherein Peter is haunted by his past and battles the darkness in himself. If that were to happen, I'd picture it this way:
1.)Set up Gwen in the first like they did.
2.) Introduce Mary Jane in the second in a smaller role (which is apparently what they're doing anyway) while simultaneously establishing Norman Osborn as a potential threat down the road (controlling Electro and all that). Eddie Brock also shows up. It may seem too early on, thus frustrating fans, but introduce Peter to the symbiote (Maybe in this story's iteration as a creation of OsCorp). He battles Electro and decides to rid himself of the symbiote because of how it's changing him.
3.) Green Goblin is the main villain in the third film. He kills Gwen and Peter goes after him. Meanwhile, amidst all of the pain and suffering Peter endures at the hands of Norman Osborn, someone keeps attacking Peter from the shadows without setting off his Spider Sense and it unnerves him. After Peter defeats Green Goblin, reveal in the closing scene that the person attacking Peter has been, of course, Eddie Brock who has somehow become Venom.
4.) Mary Jane becomes the main love interest for the final film as Peter battles Venom, who knows everything about him.
That's all convoluted and certainly contrived, but I feel like a lot of ground could be covered nonetheless. That's all if they're still going for the Venom storyline. Personally I wouldn't mind it if they didn't do Venom at all and instead opted to end the series on Peter, after suffering so much loss, opening the door to Mary Jane and the famous "Face it Tiger, you just hit the jackpot" line. That's out the window now, obviously, but even so.