As i am new to league of legends, i had hella fun playing urf, since i could practice learning how to aim properly. In normals or bots, you could use spells in a limited period of time, in urf i could do as many times i want. so urf was kind of an experiment lab for me, i could hardly lanf heims w-ult on a champ, now since i played urf, i got a bit better.
Playing so much in the urf made me forget the fact that there is something called "resource" like mana rage, etc, and that those are not infinite. Right now after playing a bot game i realized how much i depended on teleports, now walking takes too much time.
Op champs? i wouldnt say any, just because it depends on how much you can spam the abilities, but i loved playing against a zed, he was toxic, but hey, cant blame the champ for its sneaky skills lol.
I would say most of the adc category was useless or not so bright like the others, except a certain few like vayne, ashe, ezreal (but he is mostly ap), etc.
[slayer-jinx-wink]