At the end of Amazing Spider-Man, when Peter broke a promise he made to a dying man to get back together with a hot blonde "because it's fun," it totally torpedoed any ability for me to see that character as a hero ever again. But when you really think about the beats of that story, it actually makes a lot of sense. In the original Lee/Ditko origin of Spider-Man, he got super-powers and then used them selfishly until he realized his selfish actions directly contributed to his uncle's death. That was the moment when he was forced to accept the great responsibility that must also come with great power.
In the Amazing Spider-Man movie, they keep the part where his selfishness contributes to Uncle Ben's death, but in their mad scramble to change little things here and there so we'll forget we already saw this movie ten years ago, they left out the part where he catches the guy and realizes that he could've prevented the whole thing (through the less flashy superpower of being a little less douche). They left out the most important part of Spider-Man's origin, and to their credit (though this was presumably quite by accident), they did a very good job of showing just how much it diminishes him as a selfless, responsible hero without that crucial component. If we don't learn a lesson, we're doomed to repeat it, and Peter does repeat the mistake that caused Uncle Ben's death, with a similar consequence; the death of Gwen Stacy.
In the movies, I guess the story is that he's impelled to heroism simply because the tragedy of his uncle dying makes him think about things more seriously (or something?). But without the pivotal moment of him finding out the guy who killed his uncle is someone he could've stopped before it happened, there's still a part of him who's stuck in the time when he let a robber get away simply because it didn't concern him. And, unfortunately, they all-too-accurately portrayed what a person in that mindset would do with the decision to either keep a promise made for somebody's protection, or hook up with a blonde babe. Thus, having taken out the crucial component of Spider-Man's origin, the folly of Uncle Ben's death was repeated. The worst thing is, I don't see any indication that he even learned the lesson the second time somebody close to him died as a direct result of his actions.