Abbadon is so ridiculously good...
He can do everything.
Look at his level 1 stats: 600hp, 60 damage, 2.3 armour
Then you get his shield, even at level 1 it's donkeyballs. On application it removes almost all negative debuffs. Then it blocks ALL damage up to the 110 threshold at which point it returns it in a massive AOE. The best part, cooldown is almost nonexistant (hell, the duration of the shield is longer than the cooldown at all levels) and the mana cost is so low. Especially combined with the fact that this guy has such good int gain.
So can you imagine level 1 fighting this guy? What on earth are you supposed to do? Every 12 seconds he basically has immortality and if you try and fight him, you will die.
Oooooh, and then there's his passive. ANYTHING you attack, will grant you and anything else attacking it a whole crapload of buffs. So if you're running away from a 5 man gank? Whack a creep and get free haste for 5 seconds. Chasing an enemy? Whack him, slow him, and give your whole team haste. Works on towers too.
Everything about him is batshit insane. His Q is such a good INSTANT nuke and also heal. His R is crazy. Basically he ain't dying unless you 5-man gank him and chain CC until he dies.