Saw this last night.

Well I agree with you that the casting helped it immensely. I found it had some great sequences and was a pretty solid film overall.

However, it veered towards melodrama at the end, eradicating its neutrotic vibe that it had in the beginning. I also found it cluttered with the subplots of the girlfriend and his best friend and his mother's friends etc. I understand how Dan Harris was trying to create issues that teenagers dealt with especially around the context of a tragedy but I felt he tried to do too many things that didn't exactly have the emotional resonance that it should have had. 

The character of Tim, played by Emile Hirsch also felt like he was dithering between a worldly teenager who knows his predicament is temporary and a victimised one who finds no hope. It can't be both, especially since those frames of mind are definite and not analogous.

Finally, the ending was a little too much as well as too little. So the revelations came thick and fast but where was the impact, the fallout? If slightly longer with a bit more tightening, I think we would have had a gem on our hands.

Justin