I really dislike champions where "the champion plays me" rather than "I play the champion". It doesn't matter if I'm a good player if I'm playing Soraka, Taric, Sona, Annie, Malphite, Nunu, Shen, etc. These champions require very little mechanical ability, and there isn't too large of a decision tree either. And several of them have very little playmaking potential, too.

Whereas for example, Zyra, my most played champion, is probably the most mechanically difficult support. I am top 5 in terms of Zyra players in the world, and there are still times where I mess up spawning my plants under pressure. Sometimes I'll get focused and try to get all of my abilities off before I die, and I end up not spawning plants at all, or spawning the wrong type of plants. I even had an embarrassing moment yesterday where I went to QW harass in lane and my W "missed" and I didn't spawn the plant because I predicted the enemy to juke into the Q, but when they didn't juke I put the W where they were still standing. Under pressure in teamfights, it's actually really difficult to get off the ideal combination of QW EW. Beyond that, Q and E are hard to hit on mobile targets and R requires some thinking for where the circle does the most "zoning" or coverage in a teamfight, place it a bit behind a Tristana or Kha'zix to knock them out of their jump, place it closer towards you if you expect them to dash towards you, etc.

Now in terms of really "fun" champions, I like champions which have low cooldowns and lots of decision making. Karma and Nidalee are two of the most fun champions in the game, because their cooldowns are almost always up and everything you do requires a lot of important thinking and mechanics. Nidalee not only has "6" abilities if you don't count her transformation as an ability, but they're fairly different and the speed at which you string them together is important. For example, maybe you pounce, go to human form, and throw a spear. Your cursor was where you wanted to pounce, and then immediately at the flick of your cursor you throw a javelin where you expect the enemy to walk. Two vastly different cursor locations, and the precision of the javelin toss accuracy is incredibly important.

Whereas, for example, I don't like Annie even though she is a damage dealer with playmaking potential. Do we engage? If yes, then flash and roll your face across your keyboard. If no, then sit in a bush and let someone walk into you, roll your face across the keyboard, and acquire 300 gold. There isn't much room for someone to be "good" at a champion like Annie. You can be bad, but there isn't much in the way of "high level Annie" play. You can do things like E while Q is midair for an "unexpected" (not really) stun, such trickery. But a challenger Annie main won't really be better than a platinum Annie player, for example. The entire rank differential there will come from general game knowledge and decision making, absolutely nothing mechanically.