They ended up going with a simplified Diablo II
skilltree system, and what's really impressive is that they admit that it doesn't quite work just yet, and here's all that's wrong with it
. You don't really see companies telling us how much something isn't working just yet, and we applaud Blizzard for being so forthcoming. Now just tell us what the other two classes are, dammit!
They also talked about the new Rune System, that can completely change the gameplay of a skill. You slot runes in a skill, and they dramatically effect the way that skill works. Also, the runes aren't locked in once you use them, you can take them out and put a new one whenever you feel like it. Runes also come in tiered and rare flavors, and they'll definitely be sought-after items. They don't have class-specific Runes right now, but it's something they are considering adding.
They showed a few gameplay videos they show how the runes can tweak a skill/spell. The wizard can use Teleport to jump in short hops, which is farily self-explanatory. Put the Striking Rune in, and now every time you hop you do damage to the surrounding enemies, and so on. Slot the Multistrike Rune in with Electrocute, and then you can channel the electricity through multiple enemies. It's meant to literally make you change the way you play as you come across different runes, and we like the fact that you can pop them in and out, which will encourage experimentation. We can't wait to try Disintegrate with a Power Rune.