I'm... mixed.
I actually think they made pretty good use of Hannah, at least when I take into consideration how I thought they were going to use her this season. When they announced new cast members, my fear was that they would pull a "HERE IS HOW HANNAH INTERACTED WITH THESE KIDS that we'll somehow consider worthwhile even though they weren't relevant enough to include on the tapes". Using the flashbacks to fill in certain blanks with certain characters, challenging her POV as a (somewhat) unreliable narrator, and also using her to work out Clay's unresolved feelings were all the right play.
Clay, however, I feel like they made into a bit of a *****e this season. He had a few slip-ups last season, but overall, his heart was in the right place. Now he's pushing Jessica to testify, when last season, he made it clear that he'd do whatever she wanted with the tapes. He's acting possessive over Hannah and practically s***-shaming her for having a romantic past. He became a bit self-centered. On the other hand, I think the Clay/Justin relationship might be my favorite part of the season, and at least slightly redeemed him.
Tony... yeah, I don't know what that was. The whole thing of being afraid that beating the **** out of a homophobe might come back to haunt him was just an unnecessary wrinkle IMO. Especially considering he barely got any quality time with Clay this time around.
And the Tyler of it all, I'm a bit split on. On the one hand, it was well-performed, very disturbing, and almost what I would consider to be the "Hannah" story of the season, where it starts out well enough and then just gets worse and worse until things explode. But on the other, I'm not sure I understand why they needed to put him through all that hell just to get him to the point where it was pretty heavily implied at the end of S1 that he already was.
In fact, I think they could've kicked the season off with the shooting actually going down, Bryce either being killed or catastrophically injured, and the whole of the season being that his family/the school is striking back against the "smears" against their son/star athlete.
I don't know. I can't say with complete certainty that this season was entirely necessary or that it would've been better for the show to have just been a one-off. I'm just very mixed.