Saw this a few days ago and just got my internet back working.
It was bad, but I still enjoyed it because I was smart enough to turn off my brain before entering the theater. The main problem is the same problem X3 had, too much stuff going on and that ruined the pacing. The second was that the acting, plot, and characterization were more like a saturday mourning cartoon than a film. It was fun to see the classic team up of villaind and super heroes but it really ruined alot that the other two movies built up.
When ever I watch a movie I usually immediately think what would have made it better and assuming most have already been said about the movie, I'll just go right into
What Random Would Have Done
Spider-man 3
First thing, get rid of Venom. Now I am not a Venom Hater nor am I by no means a fanboy. Venom was forced into this movie which ruined the pacing and to make Venom a good movie character he (and the suit) needs more time to be explained and developed. I'll go into how to make Venom work later.
Second thing I would do is get rid of Ben's killer subplot, it was stupid and ruined one of the greatest origins in comics and with out the suit, its just stupid. Also with a villain that Peter has no emotional investment in we could have a lot better situation for classic Spidey banter, the banter they had felt really forced and stupid. From Sandman I would play up the aspect of a con on the run with a sick child it worked great in Prison Break and the barely explored this dynamic in the movie which would have been a lot more interesting than emo boy. Have scenes like the police talking to the wife and child, things like that and make his daughters situation be much more depresate, like she is going to die soon without the money, and after being constantly stopped by Spidey he gets desperate and takes hostages like in John Q for example, in the final act (more on that later).
For the MJ side of things I would have just played up the falling in her career and the success in Peter's. This creates some jealousy and doubt about their realtionship, which in the end things get settle and she realizes that she is being stupid. (She was really unreasonable in the movie).
For the Harry aspect instead of losing his memory after the fight (I didnt kinda like the throw back of classic comic book retcons) he just gets even more pissed off that not only did Peter beat him, but Pete also saves his life. I would have Harry kidnap MJ as Goblin which freaks her out, but he just hides her to lore Spidey to fight him at the mansion. Now for this fight I would have given a Anikan vs Obi-wan feeling, Friend vs friend. Peter really doesnt want to do this, Harry is his friend, the fight is just tearing him apart inside. The fight ends when Peter uses a large amount of webs to tie Harry up and they have a vocal confrontation where Peter finals tells Harry exactly what happened with Harry yelling "Than why wouldnt you have just told me?" Peter tells him that last thing Norman said "Don't tell Harry" (Seriously why didnt they put this in that scene). And Peter goes on about how much Norman loved him and Harry is just in silience, Peter asks where MJ is and Harry tiredly tells him.
Now for the final act with Sandman taking hostages, same setting just maybe a bus load of people in the building traped by sand. I would have the military start attacking first but ultimately gets defeated. This is where Spidey would step in, he wonders whats going on with Sandman why is he doing this he is just a criminal. The fight goes on but eventually Sandman starts beating Spidey (much like the part where Venom was holding him down) This is where Harry shows up and helps Spidey. (The Super hero/super villain team up was cheesy but fun and we dont really get this in movies so I would keep it). Spidey and Harry eventually weres Sandman down but he gets a hold of the board and intends to impale Spidey and Harry takes it instead. Spidey throws a bomb into sand man and immediately takes Harry to an ambulence. Spider-man now fights Flint with a vengeance until finally Sandman is too exhausted to barely hold himself together. Spidey asks him why he did all this and we get a heart filled confession from a man who feels he failed to save his daughter, Spidey convinces Marko to turn himself in and promises he'll do whatever he can for his daughter.
Peter goes to Harry's hospital room and finally get closure on this whole thing, Peter ask Harry for one last favor. We see Marko walking into a prison and he sees on tv a news reports stating Osborn industries has paid for the Sandman's daughter's operation and Flint enters jail proudly. The movie would end with Spidey proposing to MJ on a building top.
Spider-man 4
The thing about the third movie was that they barely explain the suit or gave any real importance to it. I've always hated the "hero becom es dark or emo or whatever for whatever reason" so I'll just stay way from that, I would just add Spider-man chasing down a crook and pictures his Uncle's killer much like in USM. Now for the film I would choose Electro as the villain until Venom shows up. Mainly because he can be really powerful and the only way Spider-man could defeat him is with the suit. Also Brock need more screen time and set up, at the begining of the movie he is on top but is yanked down and just a bunch of crap falls on him. They had him getting fired in a good way, I would rework how he loses his girlfriend, but he needs more taken away, like being evicted from his apartment, etc.
About the suit I would have it react more like in the comics how Peter doesnt take it off but hides it underneath to close and play up the "living" aspect. Everything else just needed more time to develope than thrown in. Like the church scene felt really rushed and it could have be so much more dramatic and so much better. Have Peter start questioning his behavior and really get dirty with him pulling it off. That would have made a powerful scene and I hated how they intercut it with Brock in the church, I would just wait until after Peter gets it off before the Eddie scene. Now we need Eddie taunting Peter for a few scenes before kidnapping MJ showing every reason why Peter didnt want to date her. They really need to play up the Spider-man vs Dark Spiderman aspect there wasnt nearly enough to satisfy me. Just more is about all I can really think of right now.
There's probably more I wanted to say, stuff I left out, spelling mistakes but right now I'm just tired of typing.