In terms of what happened I have some fairly mixed feelings. Zimmerman should have listened to police and stayed in his car. He was Neighborhood Watch and one of the main tenets of NW is "do not get involved". You are always instructed to call the police and let them deal with it. You are there to be an extra set of eyes to watch things, not an extra set of hands to shoot people. This guy was not trained to deal with this type of situation and should have waited for the police to come. He called the police and he should have let them do their job.
While people are trying to paint the kid as being a bad seed or a thug I think that is probably fairly far from the truth. While he is certainly not the model kid (he was only at that particular house because he was on suspension from school) he was probably just a kid whose parents are divorced and going through a tough time, not unlike a million other teenagers. What a shock that a teenager kid was smoking pot....... truly unbelievable. I don't think he deserved to get shot.
What I believe probably happened: Zimmerman chased the kid, yelled at him, threatened him until the kid finally had had enough and turned around to face him. They probably tangled a bit and Zimmerman (whose pants and underwear should have absolutely been checked since I am sure he soiled himself) was getting his ass kicked, took out his gun and shot the kid. There was a witness report that Zimmerman was sitting on top of the kid after he shot him which is very possible if the kid was initially on top pounding on him and then Zimm shot him and sat up.
I don't buy the police video that shows no marks or blood on Zimm (you can't see ANY detail on that video), but I also don't buy that Zimm was in any real mortal danger other than on the receiving end of an ass kicking by a HS kid. It was self defense, but not in a way that Zimm needed to shoot an kill the kid.