A lot has changed, and although we probably know about half of what's changed, we don't know all of it.
The skill system was redeveloped, class advancements were added.
Dungeons were hugely revamped with platforming and traps.
There is like 3 or 4 times more content then there was in alpha, and just so much more.
I recommend browsing through the forums or the fansite:
For more info