Classes and Skills are more liquid in this game than in Diablo II. The Ascendancy class is the most important choice, I hope it will give you a fun playing even if your character so random skills that make little thematic sense.
e.g. I'm playing a Duelist, but all I do is hit my enemy with sword/axe, seeing 4 Balls of Molten Magma hitting anything around it (but me).
I really looking forward to that Ascendancy class, and I'm certain to choose assassin. Eventhough this game put me in a rather funny start with everything, I am having fun with PoE.
I have that magma balls ability too. I was kinda confused (with the design, I guess?) but also having fun looking at the mobs keep dying from it.