On my Fighters and Rogues, attacking from behind usually means I get at least 80% chance to hit. It's the same for ranged characters shooting from high ground. If you're getting 60% even when attacking from behind or from high ground, you're doing something very wrong. Take a picture and link it here, and we might be able to point out where you went wrong.
The same for me, that isn't the issue. The issue is that it isn't 80%, the issue is that it shows you it's 80% but try reloading ten times and see how many of those ten times you actually hit. I assure you, it's not even close to eight times out of ten. That is one of the issues.
The second issue is that the AI has a nigh 100% chance to hit, definitely above 90% no matter what their position is relative to you. That creates a disconnect, i.e. you take damage, the AI does not.
The third issue is that the AI on average hits for more than you do. You might hit an 8, they'll hit a 12, for example. This makes missing all the more problematic because by the time you hit you're close to death.
The forth issue with combat is the spell slot system. I understand the need for something to stop you spamming your most powerful spells but of all the methods I've seen in games down the years, this is the most restrictive.
So you take all these issues together and you have a situation where you miss far more than you miss in other games, but get hit as much as you do in others, which means as a fighter you're taking too much damage too soon, and as a Wizard you burn through your available spell slots, rarely connecting with the target, and the sole way to regenerate all your spell slots is to have a long rest at camp, which you obviously can't do in the middle of a fight.
I want to be clear again, I've been hammering the combat system, getting into fights and trying them with differing tactics and weapons. It has nothing to do with those, the problem is, I believe, algorithmic in nature, i.e. the numbers are off because the AI isn't playing by the same rules as you the player are. In short, all these issues together are creating a combat system that is simply not fun to play.
