BG 2 had one of the best villain in gaming history.
The best thing about Irenicus is his memorable voice acting, but apart from that, he is a very milquetoast villain. A powerful elven mage punished for his thirst for power, yawn. The only unique thing about him is his sex dungeon.
He gets his job done because, at least, he gives you a reason to go after him from the very beginning of the game (and some more recent examples showed us we can't take that for granted), but I don't understand what could possibly make him "one of the best villains in gaming history".
I won't argue that Irenicus is the bestest!! villain ever.
But I disagree that he's "passable at best".
He has simple goals and his motivation is clear.
Which is already better than dime-a-dozen obscure ancient evils, bloodwar demons, repears and tyranical overlords.
He is shown not just as immensely powerful wizard, but as a schemer who calculates multiple steps in advance and places agents in key positons.
Perhaps his lust for power was the reason of his exile, but it is not what drives him in the game.
Even though he is dying, he does not stoop down to soulless solution Bodhi had chosen.
And then there's the revenge part. And bits of tragic love.
He is pretty multifaceted character, not a cardboard mannequin for the protagonist (and the player) to hate.
So unless you can list droves of better villains, Jon is certainly in top 5 in my book.