I admit I'm working on a slight disadvantage here since I only ever saw the movie once back when it came out on video and never since, so a few details may be escaping me. Nevertheless I think you could safely edit out all the Eddie Brock scenes with minimal impact on the rest of the plot. Certainly everything after Peter rids himself of the suit. Indeed, it may have been way more effective to leave that as foreshadowing for the next movie.
With the exception of Angel in X3, I haven't seen a character so superfluously inserted into a comic book movie. it had "studio mandate" written all over it.
I have seem the movie a few times and I think it's a little too interconnected to remove. That's why I'd argue that, for a studio mandate forced on the movie, it turned out better than could be expected. It may make for an overstuffed movie, but it does read as one movie and thematically fits, instead of two movies mashed together that have nothing to do with each other (like say ASM2 or Iron Man 2).
(Actually, as I understand it, there was some discussion of splitting SM3 into two movies, but there was no consensus on where the break off point should be. Frankly, I think you're mostly right; end part one with the scene were Eddie gets the symbyote and then make the A plot of part two be him trying to get revenge of Spider-Man, with the B plot being Peter and MJ healing the rift between them. However, given that Sony chose to reboot after three movies, maybe it's just as well that Raimi and company played it safe and left SM3 as one movie. While not maybe the ideal movie, it's still a complete story in and of itself and gives the trilogy a definite ending. Had they split the movie, there's a good chance that the series would've never had any form of closure.)
The main problem with the Goblin storyline is that it entirely skips a step and goes straight for Harry donning the suit and out for blood. Yes it builds on the cliffhanger of SM2 but it does so so very poorly that his first appearance feels astonishingly perfunctory. Which for a well established character is so bizarre it shouldn't even be possible. It's all very awkward and poorly constructed.
Some of that may be blamed on needing to make room for Sandman and Venom, but we can only judge the movie they made, not the one they probably should have.
Can't say it ever bothered me much, but then again, Harry Osborn was not exactly among my favorite parts of the series in the first place.
MJ may have had more to do on paper, but the end result left no lasting impression. Just more overwrought, forced relationship drama that was more about Peter than her anyway. Indeed, as I understand it, Dunst was quite sick of the role by the end of it and I can't say I blame her.
Well, Peter is the lead character in the first place, so the stories ultimately go back to him. Beyond that, I guess it's all subjective. Besides, the relationship between the characters was put front and center from the beginning, so it would be expected to be a major part of the story here.
Not tacked on in the sense of the progression of the final film's story, but in the sense of the progression of the creative process that led to that story. IIRC, Raimi had wanted to make a film with Sandman as the villain, and Sony insisted that he add Venom as well. Naturally the rewrite of the script incorporated the symbiote, Brock, and Venom throughout the entire plot, but it was still a thread added on to the originally intended storyline, and it made the plot more cluttered than it would otherwise have been.
Fair enough, but, as I indicated above, I think the movie made it work better than it could have been,
Overall, ASM2 was hardly good, but its treatment of the characters of Peter/Spidey and Gwen Stacy (and Aunt May, to a degree) was excellent. That's the tragedy of it -- you had a couple of really well-done characters in the middle of a generally poorly-done movie. This was the best screen rendering of Spidey I've seen -- he had the attitude, the wit, the nonstop motormouth. And ASM2 actually let him play dramatic scenes as Spidey, with the mask on, rather than making excuses to get the mask off at every opportunity.
Fair enough. Not sure I entirely agree with you, though.
May was good, just underused. I found Gwen to be a badly-written character played by a good actress. which only goes so far. Peter might've been okay as is, but I found the character is not a good representation of the character from the franchise proper. Specifically, the movie was based on the
Ultimate Spider-Man comics, and, having followed those, I think I can say with some authority the movie Peter and Ultimate Peter are not the same characters. I also found Peter in the movie to be an unlikeable jerk.
As always, your mileage may vary.