Thought we should have a thread that focuses on things we learn about the classes in DF 2.0. I'll start off with some things I have picked up playing the Elementalist.
First up, when you hit the <tab> key to load up your radial dials with skills, there are skill at the top of the screen, and at the bottom of the screen. As a mage I focused on the bottom skills, as the top ones were always red and would not load when I switched the focus to that dial. I discovered that this is because I lacked the reagent to cast those spells. That reagent is Elemental Dust (or something to that effect). If you have this in your inventory, you can switch to one of the Elementalist spells. Goblins drop this reagent, but my experience is that Trolls drop this more often.
As for the spells themselves, I have played with Fireball the most. Against goblin scouts and warriors, fireball does as much damage as the basic mana missile. Against Goblin Shamans it does a bit more, but not enough to warrant the use of the reagent (IMO). Against trolls, a fireball will one-shot them. In fact, it appears that just the splash damage will kill them instantly. The Trolls are much more resistant to Mana missiles. I don't know if this is just a higher amount of hit points or that they are super vulnerable to fire. The trolls hand to hand attacks tear me up pretty quickly, but the magic seems pretty weak, so keep your distance and you will be fine.
For the goblins, mana missile seems to be working well. In two days of playing my 'staff skill' is up to 42, and many of the goblin scouts are dropping after 2 hits. I am finding that against scouts I just let them close to me and Mana missile them right in the head. Warriors and Shamans though also tear me up at close range, as well several goblin scouts hitting me at the same time.