Back in 1989 Drizzt was an exploitation of some first edition rules that appeared in Unearthed Arcana, but even then he was technically illegal. In second edition he was pretty powerful and also broke the rules of the game. In D20/4e he no longer broke the rules of the game, but WotC designers notoriously do not present NPCs with optimised builds, so he looks weak by comparison. Dunno what his statistics are for D20/4e.