Played it a year and some months ago. It's an ARPG like Diablo 2. It h as great complexity and freedom when it comes to character builds. Any "class" is available really, as is any skill. Total freedom of how you want to develop your character. It had some balance issues (chaos inoculation, totems, lightning damage etc.) but they've been patching it regularly so I think it should be OK now.

Watch some of Kripparian's vids to get the hang of it.