I agree, school days was actually really good for what it was trying to accomplish; It wasn't listed as a ROCO, but a tragedy and i think it fulfilled that purpose to the extreme. Its one of the few anime's that to this day still make me cringe, which says something vs the 100's that i have completely forgotten about.
As for the worst things; Revolutionary Girl Utena sticks out; I watched it because back in the day it had a rule to watch a series to completion regardless of how bad i thought it was. That was the series that changed my mind; To this day i dont know why people still thinks it was a good anime. Bottle Fairies was the first one where i got 2 eps in and said 'oh hell no' and moved on.
I actually liked school days as well. It made me hate Makoto for the perverted, manipulative POS that he was but it really did set out what it wanted to do and it did it in spades. It also felt like a breath of fresh air compared to many other series that would just end up as normal harem romantic drama. I like that it was distinct in what it did.