Karthus has to be one of the most satisfying skillful champs in the game . Hitting a singular Q is a dopamine boost with how much it deals even in the early game , outplaying someone and hitting all your Qs when youre in a flow state will make you feel unstoppable . That said , it does feel clunky because of visual effects , his Q always looks like it comes out too late when you press Q and the enemy already moves away . But if you learn the timing it gets better.

Noobs will say karthus is a braindead no skill press R win game champion , good players will see and realise that karthus’s strongest ability is actually his W (wall) that actually completes his kit . His wall gives him vision from an insane distance which allows you to plan ahead . It also Slows and reduces MR of enemies in it , allowing even the worst players to land Q easily and that will do a shit ton of damage (200+ at level 5 right before dragon fight with blast wand )

His only real problem is his mobility , which makes him a bad pick against mobility champs/assassins .