My brothers and I never read the manga, and we still hated Root A. For us, the major problem was that it didn't make any sense. No ones character motivations were really being explained, things didn't add up story line wise, and any build-up for certain characters or plot points just seem to disappear out of thin air or end with a cop-out.
Kanaki and the gang breaking into the Ghoul jail and Kanaki rescuing that one guy at the bottom, who he had to fight--which the story was making it seem like said guy was going to be important later--but then you never see him again after that.
Touka: "Yay! We rescued you Kanaki! Let's go back home now!"
Kanaki: "Nah, I'm just going to go join the guys who just kidnapped and tortured me for the past few episodes."
My brothers and I: "Wait--WHAT?!? WHY????"
There are other examples too, but I don't feel like searching up characters names to re-tell all the stupid things that happened in Root A. My brothers and I really enjoyed season 1, but Root A just ruined the series for us--yes, we know now that it's different in the manga, and maybe one day we'll give the manga a try. But the only thing that relieved our frustration with Root A was this video: https://www.youtube.com/watch?v=Ur-8ibFvAY4