So there is now a Skill Calculator out.
http://us.battle.net/d3/en/calculator/barbarianYou can see all the skills you can get for each class, a selection of runes that can be slotted in to them, your passive abilities you can buy and any additional game play mechanics like the Monk's Mantras.
Basically, other than the visual changes, prepare for a ton of "Weapon damage +75%, bleed over 3 seconds, third strike does (Y)."
It's going to take the many mechanics established by WoW, and compact them several times over into one ability. Abilities will be one half that, and one half the animation that goes into them.
On the one hand, I haven't played a Blizzard game in years now and I could probably stand for some Blizzard-style mechanics. On the other.....the design is really obvious. It's this nice, neat little bundle they've already pre-plotted to the degree they're ready to show a skill calculator. The only variation you can expect is in your gear and your rune assignment, and in the selection difference of one or two skills. Compared to what seemed like Diablo 2's much more flexible and choice driven approach....they've narrowed and iterated gameplay down to just a handful of choices. Now, there is going to be a lot of diversity within those choices....but I felt like I wasn't seeing a whole lot that was new out of Blizzard, just a further amping up of everything they've learned so far.
I'm starting to feel like what's going to be most impressive about Diablo 3 is the amount of effort that went into the Rune System and having every attack look different based on its runes. That may NOT be the case exactly, reading several of the runes, they're literally stuff like "make things bleed." "Add fire damage." Will all those get their accompanying visual effects, or will be more like gem slotting in WoW? Hard to say at this point. I'll be very surprised if each and every rune makes your attacks look visually different.