He did in the first film, too. And in neither film did he actually witness the action.
I'm pretty sure the guy in the Raimi movies was a burgler who broke into their house, while Peter was gone. Peter came back to a dead Uncle Ben, while it happened right across the street in this one. He saw the action, but he didn't realize until he got over there that it was Uncle Ben.
Except it was rather in character. At the time, he was acting rather selfish: he was only looking at ways to purchase a car to impress Mary Jane, and he acted rather coldly towards Uncle Ben before said event. It was quite clear that Peter and Ben were growing a bit distant.
The moment in both movies happens out of spite, but in the Raimi ones, it's because Peter is acting very smug and over-confident, and in the new one it's because he was emotional after having a fight with his uncle. Peter is much less of a jerk in this one, which makes the scene that much more meaningful. Acting out of spite because you're emotional is a much more human experience.
Both work, really. I don't see any problem with going either route, as one establishes Peter's mindset whereas the other establishes Peter's abilities. Both are acceptable for what they seek to accomplish.
I'll give you this one.
Well, here's the inherent problem: you're taking two different approaches to a love story, and once again there's no real problem with either one fundamentally. The issue I always took with the Mary-Jane/Peter relationship was some atrocious dialogue and, well, Mary-Jane. But Mary-Jane kinda represented a goal for Peter much more than a person. Something that seemed unobtainable before but with his new-found powers (and confidence) he suddenly found the courage to go after her. In that sense, it worked for Peter because it represented a certain level of character growth. The problem with the Mary-Jane in the movies was that she was rather static as a character and it hurt the overall development. Also, Dunst wasn't nearly drop-dead gorgeous enough to make it work.
On the flip side, we're more TOLD that Gwen Stacey is driven than we see it, and she's reduced to "worrying girlfriend" when tending to Peter. To her credit, she defies the normal "girlfriend gets captured, put in peril" plot by making her own choice to stay in the end. I had no real problem with it, but it didn't really come off as great, especially since I didn't care for most of their interactions. Basically, both are concepts that are fine, but one was rather flawed in execution and the other was just mediocre.
We definitely see it, though. She's the head intern at a major lab at age 17, which is incredibly impressive. And she's a worrying girlfriend because she sees Peter like she sees her dad, both going out to risk their lives for the betterment of the city and it's people. It's a feeling she has every day, it's just being extended to Peter as well. Gwen is a much better character because she's actually proactive. In the Raimi movies, Mary-Jane is a constant damsel in distress, whether it's from muggers, Green Goblin, or her own family, she exists to be saved. Gwen, on the other hand, is actually a very proactive character. She saves everyone in the Oscorp building, gets the antidote made, and when the Lizard is in the school, she bashes him on the head with a trophy.
I thought Garfield and Stone had excellent chemistry. That moment between them after Captain Stacy's funeral is just heartbreaking, and I was genuinely concerned that the movie was gonna end where pretty much every superhero movie ends, with the hero sacrificing love for heroism, but in this one, Gwen is the perfect girl, because she understands and accepts Peter, and his responsibility.