Overpowered Abilities
I know this may seem as I am a little butthurt, but infinite stacking and empowering of a select few champions overpowered. The main abusers of this is Nasus and Veigar. All champions have their downsides, but Veigar in particular is the main problem. With Nasus, you may need 2-3 people to defeat him, but he can be kited (still can one shot carries tho). Veigar will keep on stacking till eventually he can one shot a whole team. As Veigar, you can use 2 out of your 3 damage abilities and one shot. The assasins are being reworked to add more counterplay to them and extend their burst period. He isn't even classified as an assassin, but can burst people faster than akali or zed or any other REAL assassin. What could be done is make his e shape his dmg and that small square area of his w into the stun shape. Veigar can be too influential and even when behind he can catchup easily by farming. Veigar can go full tank and one ability power item and he will still be able to one shot carries. I'm not sure what can be done, but I think the rework he received at mid year made him so much stronger. He only worked against Ability powered midlaners, then the change to his ult made it that it increased damage on health done. Veigar is a pain, unless he isn't one shotting you.
Peace on the streets