I managed to max my embermage at level 21 for the weekend beta. Afterward, I beat all the quests, as well, and I believe I have a good idea of how awesome Torchlight 2 will be. Needless to say, it is preorder worthy.
For the most part, Torchlight 2 features all the stuff you saw in the original, gameplay wise. The one major addition is the multiplayer aspect of it. You can play with three other players, and you can host your own server very easily. The game supports offline play as well as online play, and you can play over LAN. (That's local area network in case you didn't know.) All this in addition to the growing world of Torchlight makes it easy to see why you want this game.
This article covers the Embermage class, however.
What makes Embermage OP (overpowered):
Magic user, use focus stat to enhance some very powerful and very pretty spells. Dual-wield wands and you get long range magic attacks without the expense of mana. As long as vitality and focus are very high, Embermage is practically unbeatable.
What embermage is lacking:
Defensive spells. Torchlight had some great defensive spells given to the mage class, yet the new embermage focuses only on offense. One could say that the best defense is a good offense, but in the realm of dungeon-crawlers, it can be hard to avoid getting hit.
Most annoying thing about the Embermage:
No dodging move! I hate not having a fast movement method. In Fable, it was the assassin rush. In Torchlight, it was the female class' dash. In TL2, I imagine the Outlander class has such a movement ability. I will have to check that out.