I have been mucking around with the new Diablo 3 skill calculator. Even though D3 isn't easy to model in a spreadsheet and I don't even know what a lot of the abilities do exactly I still have a desperate itch to start calculating things and figuring out what the optimal builds are. One thing I must say is that I absolutely love the design of it. You get six active abilities, each of which can have one of five different runestones. The runestones modify the abilities in all kinds of crazy ways. Some make the abilities generate more mana, some make the abilities hit harder, some add extra effects and some completely change the way the ability works. You also get 3 passive abilities that aren't modified by runestones and which aren't cast a spells but just add to or change your character.
I set out to see how flexible characters could be and I was very impressed. Check out this Tank Barbarian build. I built a Tank Monk too and they are both really powerful (well, tough) but in very different ways. The Monk stacks Dodge effects (85% !) and has powerful debuffs and self healing effects. The Barbarian has enormous health, armour and healing but his Dodge is absolutely wretched. I played around with all of the classes and I am pleased to report that in every case I was able to find many really interesting builds with all kinds of choices. I built a ThrowBarian, who is awesome because he is a Barbarian who has no melee or AOE skills at all and relies on zooming around the battlefield blasting people with savage ranged attacks and summons.
The thing that is really telling is that I constantly need just a little bit more. I always build a character and have to make difficult tradeoffs like deciding if I can allow myself to build a Wizard without Teleport. Who can play without Teleport?!? but yet if I cut it I can set myself up to do more damage and be more flexible in combat. I liked the Witch Doctor as a summoner using stacked AOE debuffs and Blizzard seems absolutely savage as the Wizard but no matter what build I try I am always rebuilding it trying to figure out a new way to squeeze a different ability or extra effect onto my character.
That is a good sign. I suspect you will see huge variety in character builds in D3 because so much of the build is a judgement call. Are you good enough to be able to drop a defensive ability for another offensive one? Can you afford to drop an ability that generates mana to get more utility or will that additional downtime be annoying? This design is much, much better than a talent tree like D2 or WOW boasts and for my money is the best character customization design for a pure combat game I have ever seen. It is very easy to get started and make some reasonable choices and understanding the rules of the system is trivial but finding the absolute best build is extremely difficult.
Easy to learn, hard to master.