Its probably old news, but the passives tree is VERY similar to how the sphere grid of FF-X worked, and the active skills seem very similar to how materia worked in FF-VII.
One passive grid for all classes, the different classes start at different locations. Classes are loosely tied to attributes: STR, DEX and INT, there is one class for each attribute and one class for each pair of attributes. The witch class starts on the INT area of the grid, and the duelist class starts between the STR and DEX areas in the grid. Each passive skill point lets you traverse to any adjacent node, and the nodes have things like stat bonuses and bonuses to skills.
Active skills are based on gems that are slotted into equipment. If you want to cast a fireball, slot the fireball skill gem into something your wearing (provided you meet the stat/level pre-reqs). There are regular slots in equipment and there are slots that are linked to other slots. Regular slots just allow you to use the skill, nothing special, but linked slots establish a relationship between the two gems that are linked. If you were to put a cleave skill gem in a linked slot and attach an added ice damage gem into the linked slot your cleave would now do ice damage. The gems that are slotted into the equipment your character is wearing gain experience and level up as you kill enemies.
I havent played in 2-3 months at least, but it felt unpolished (as you would expect from a beta) and I was not a fan of how selling to vendors worked, however that was implemented just days before the last time I played. The general feel was nothing spectacular, but the mechanics have massive potential IMO... so much so that I think if done right, I'll be enjoying this one more than D3. That said my expectation remains kinda low, still in the wait and see phase.