I played ADnD 2nd ed and I played 3rd edition (and some 3.5 via computer games) and I have to say, Thac0 was a horrible system. 3rd edition is not responsible for the removal of a rigid class/race system, modernisation is, evolution is, or as some people would call it "natural progression."
I don't understand people who claim their system was best and the modern ones suck, because I bet they use watches and not sundials, or use gps/satnavs instead of navigating by the stars. Thac0 was a HORRIBLE system and I am glad it got put to bed when they introduced 3rd edition rules, also changing rogue (can't say I understand why thief became rogue though) skills from a % check to being just a skill check.
On Topic: There are no classes in Divinity: Original Sin, there are merely premade characters to ensure people don't have to think too hard if they want to dive right in to the action. For the rest, you can mix and match what you fancy taking.
The chat system is handy to ask people for help if you get stuck, because sometimes you don't want to spend hours trying to remember who gave you the quest in the first place to hand it in because the journal misses a lot of that stuff out sadly.
