I think the main problem is the freedom in the game. There are too big differences between playing styles.
If one is playing 'normal' with hybrid characters and another one is crazy killing every NPC and has single class characters, the second gamer will have much more XP and can have stronger characters.
Theoretically.
However the RPG experience is different in both cases.
In such freedom the game cannot track how people play, and cannot dynamically balance during gaming. This would be but nice!
