I don't like URF.
Now hold in your appalled gasps for a moment; I don't HATE URF. I like how fast paced the fights are, and how silly some of te games can be, and I'd still take URF over Poro King. But I'd like to explain my point of view given how much I've already been crucified for not liking URF on the Rift.
1. The novelty has worn off
I played URF during it's 2 week lifespan last year and greatly enjoyed it. The key difference between then and now is that I'd seen it before. I'd already squeezed all the enjoyment I could get out of the ridiculous buff. To enjoy URF now, I need to enjoy the actual gameplay, rather than just the fact that it's insane gameplay.
Pretty much every URF game I played last year and so far this year have stomps. This is likely due to the winning teams have more gold, can get more items, which make their abilities stronger, which (because its URF) makes it damn near impossible to beat them because they have no downtime for you to outplay or exploit, so you can only fight them straight on, where they have advantage. Some people enjoy stomping and that's cool, I just don't. Being stomped in URF means you barely play the game as you get dove and nuked over and over again, and stomping in URF makes the game require next to no thought and to me, makes it boring. I like games that are tense and close, and thay rarely happens in URF.
3. The very nature of URF seems backwards to me.
Despite what some say, Riot does take care to balance League. They take time to ensure champions have counterplay, be it through long cooldown where they can be countered, or high mana costs to stop spamming. URF takes all these measures to keep the game fair and not frustrating and sets them on fire. Pretty much every opponent I've faced in URF this year has been some of the most frustrating laning I've done in my life. Facing Fizz who spend more time undamageable than damageable, Nidalee whose spears hit loke a truck and never stop coming, Alistar perma CC, Swain never dying, Nasus killing towers in 2 seconds. While playing as these things is fun, playing against them is so frustrating I don't want to play the game mode.
3.5 Some champions are unplayable.
URF is essentially "Which champions abuse the URF buff the most?" If a champ u want to play doesn't abuse the shit out of low CDs and no mana costs, you are almost guaranteed to get dumpstered and stomped, which makes for games where everyone picks the same champions who abuse URF's rules.