I can finally say this! The biggest problem I've encountered (save for quest bugs which I'm sure will be fixed) is that there's no indication you've hit a target or done damage save for watching the target's health bar. That works fine in PvE when fighting one or two enemies, but in PvP you often can't see if you're hitting anyone.
The problem is especially obvious when using a bow. You can't tell if your target is out of range, has moved just out of range, or sometimes even if it's in range due to low damage, meaning you hit but can't even tell. When casting spells it's pretty obvious a target is out of range because you can't cast. But bows - and I guess melee weapons too - can be fired regardless of range and so you need some visual indication you're hitting something.
There's a PvP review video where the reviewer is using a mod that shows floating damage numbers, exp gain etc. but that should be native to the game, not requiring a mod.
Even when using trebuchets vs walls and doors I couldn't tell what kind of damage I was doing or if I was hitting nearby enemies with AOE damage.
It didn't take away from the enjoyment of PvP but it made it a bit more confusing and more of a guessing game than it should be.
EDIT: The numbers themselves are not important. It's the fact that they tell us we're hitting or healing that's important. If our reticles changed color when we did something (say red for damaging an enemy, green for healing a friendly) it would be fine because all that matters is getting visual feedback in combat beyond tracking tiny health bars which can get damned cluttered in mass PvP. Floating numbers are just a MMO regular feature by now so it's what I thought of first.