One of the things that bothers me (and I haven't seen it mentioned) is how experience is handled.

I feel like the "getting experience for killing" is a highly limiting approach - it enforces the mindset of "kill first, speak with dead later".
While there were moments during exploration where I was given some amount of experience, I have no indication to suggest that the "diplomatic approach" give me any experience (I legitimately don't know if you get experience for that - I did not look it up and, as mentioned, there was no indication of it happening in game).

Another thing to note is how experience that is earner (the actual method is irrelevant) gets distributed. There are several ways that I have seen this to be handled:
1) Global type where the progress bar is the same for everyone ensuring that there is zero disparity between all of the characters. This, I believe, would be the best option since multiplayer exists. And even in single player, it would be preferable to NOT have a party member that is 2-3 levels behind (I don't actually know if the party members that stay in camp get any experience, because I only had 4 people for reasons beyond my control).
2) 'Follow the leader' type, which is similar to the Global type, but where the "main character" has a marginal lead over everyone else (who are otherwise equal to each other), however, not a significant lead (5-10% ahead). Dragon Age uses this method, I believe. This ensures that "your character" is always equal - sometimes superior - to the rest of the party, however, this won't translate well to multiplayer, so it's not a valid solution.
3) Individual experience with various degrees, such as only active party members, only living party members, etc. In some modes of play, such as solo play - even though the 5e ruleset should not allow for it, from my experience - this is preferable, because the idea is to have a single character that is significantly ahead of the curve. This is a fairly common approach to such games, although not everyone enjoys it. Pathfinder Kingmaker seems to have made a good - if obvious - compromise: there is a setting that changes between "global party experience" and "active party only".