There are 4 difficulties: Casual, Normal, Veteran, and Elite, and in addition a hardcore mode. Can be seen on this video at around 2:50.
As the official site states:
Since there are no real benefits for picking hard difficulties other than fun (you don’t get better loot), you are free to play the game how you most enjoy. If you like being overpowered… you can play normal mode. If you like a serious challenge, play elite (which is much harder than very hard in TL 1). If even Elite is not enough for you, you will be able to easily download a difficulty mod and challenge yourself further.
The loot and drop rates don't change, only monster health and damage change.
And there is always the option to create your own difficulties with mods, to suite your specific desires.