For me the biggest downside atm is the getting xp only on quests.
I fear this will make the game very linear and perhaps even force you to complete quests you don't actually like on every playthrough, simply because you have no other choice on where to get xp.
Imagine having to do candlekeep chores every time you started a new game.
Or having to backtrack the whole dungeon, simply because you find out you aren't strong enough to face the final battle. Especially now that they plan to make damage spikes and combat less random, (which i also thought gave a lot of replayability to the IE games) so your stats will most likely be what dominates on whether you win or lose.
From what i hear the xp system is implemented to prevent powergamers from killing everyone once they complete the quest, but you could easily fix this by simply taking away the majority of the xp from the quest giver after the player completed the quest. After all, xp is subjective.
I don't know what the update on weapon/armor types are but last i heard there was a chance, you would need to keep switching weapons vs different types of armor, even in a single encounter, or face a 50% damage penalty. It feels a tedius shallow mechanic.