[psquid]

He's not so much a great programmer as a productive one (not that those are concepts that can't coexist, he just isn't both).

He's very good at taking an idea and making it work, then building new stuff on that, but less so at actually making things robust in an architectural sense. Moving on to the next thing that interests him also doesn't help that.

A lot of the biggest hiccups in Minecraft's stability are more-or-less directly caused by having to work around stuff that was coded in a way that made sense at the time, but gradually fitted less and less well to the game as it now stood.

I'd say at this point a lot of Notch's original code is outright gone, and that's a good thing. His vision is still at the core of it, and that's what he really brought to the project.