Nerfed or Underpowered Champions
I'll start with this in alphabetical order.

P can deal beyond 600 damage per meep (4 or more) in late game. With slow and area effect. Q deals little to no damage, possible stun, and a obvious slow if hit. W lays down a heal that heals a smaller amount than Taric's Q. E lets you travel a ways through a gap. (WHY CAN'T THIS BE A FREE SPELL!?) R stuns allies, enemies, everything if hit, but they are untargetable.

P allows bonus damage or pets to deal bonus damage. Q either sends out a little damage or some damage as the spider. W sends out small damage in an area or again small damage as the spider. E stuns an enemy or allows her to travel to an enemy with no hassle. R does the change.

P allows better cool down. Q deals damage or with R, better damage. W deals damage with a snare, or with R heals with a better snare. E allows a shield with ms, or with R better shield. R allows a better ability.

P allows some bonus damage and retrieves a small amount of energy. Attacks cool it down faster. Q deals a small amount of damage, but gives a nice health regen. Not a good heal if enemy dies though. W shields for a small amount. Passive does not work. E deals damage if it hits, reduces damage, and taunts. R transports him to an ally, not shielding Shen or giving him a means of going back.

P gives back 4% health per ability. Can revive up to 50% health. Q deals a small amount of damage, and slows. W sends out small damage to those near him. E allows Zac to fly to a location. Those hit receive a lot of damage and are sent back. R deals only so much damage, and allows only 1 knock back.