Just watched it...
Truth be told, I didn't like it much either.

It seemed kind've cliched to me, didn't feel like regular Tree Hill. It was a very by-the-books school shooting episode. Most of the hold-up scenes in the library didn't grab like I thought they would. High points though...
The writing: Mark did a great great job. All the speeches and monolouges said, were fantastically done. The guy should write movie screenplays in the future.
The acting: Personal bests by pretty much everybody. Hilarie was the most showy, the fact that she handled it well impresses me even more than she did better. The library scene was her best ever. Bethany played a more reserved role, though she was just as good. You could see the anguish in her face. Sophia didn't have much to work with, though the pole thing was good. Chad, James(who is usually horrible), Danneell, Craig, usually I don't hold their skills in much high regard, but they all pulled it off in close to their best work ever. Guy who played Jimmy, I didn't like him early on, but his last scene redeemed himself.
Overall, most of the hold-up and episode was a letdown. But through it all, 2 of the scenes(The library, the ending) I consider some of the best in the show's history. The rest didn't quite hold up for me though. Didn't feel like the same show, it felt...different. It was generic, something OTH usually steers away from.