We're working with a modified skill tree system now of what we showed, under heavy testing and scrutiny. It's of course not final, the ideas it proposes are something we're happy with in their direction but they could very well change. In fact I would bet on them continuing to evolve.
So, the system we have now... you'll have to just picture it without any visual representation, sorry. They're not radically different visually except that the trees are all viewable at the same time. Taking the barbarian trees for instance (berserker, battlemaster, juggernaut) they're not tabbed now, but instead all viewable at the same time. Side by side.
This is important due to how they are now a unified tier progression. Instead of spending 5 points in the berserker tree to then begin spending points in the second tier of the berserker tree, the new design allows you to spend wherever you like. As long as your points in the first tier of skills adds up to five, the next tier for all trees is unlocked.
So, I could spend 2 points in Heightened Senses which is a berserker skill, and 3 points in Bash which is a Juggernaut skill, thus adding up to 5 points and granting me access to the second tier of skills for all of the trees. With this amount of freedom you can see how easy it is then to diversify yourself and your build. You're no longer gaining abilities through investment, but instead more through choice and personal preference.
It certainly diversifies the types and amounts of builds available to players, that's obvious. This style of a unified tier approach also helps in a few other areas though. Since all of the trees are open we can clean up the trees a lot more, removing redundant abilities. We don't have to throw in skills that are important, such as damage mitigation, all over the place. You will always have access to those skills no matter where you're spending, so they can instead be focused into a few key skills. Another way it helps is by allowing players access to the skills they want, and the skills we want them to have. Every barbarian is probably going to want whirlwind. And why not? What this tree style allows for, and one reason we're pretty keen on it, is that we aren't saying "You're a 'berserker' barbarian, you can't have whirlwind". Instead, you're a barbarian!, pick the key skills that define you and your character as you want them to be.
One important addition to this is the skill caps themselves. Currently we're envisioning the majority of skills to be capped at 5 points, to begin with. As a form of progression we're planning for players to be able to increase the point caps of skills. More than likely to a maximum of 15. It's a system that's still under heavy design, but the fact of choosing and increasing key skills beyond their initial cap is important to this new unified tier system.
So, once again these are things that are still under heavy design and iteration. They're changes we're testing, and while we like how they play there are certainly issues or flaws that could cause an entire switch to something else.