My problem (the bit you might care about) The biggest mechanics issue for me currently is weapon swaps, as dumb as that sounds It feels incredibly bad "wasting" an entire standard action on it; it's really taking it out of the equation because 99.9% of the time the penalty is just too harsh, so you start ignoring the theoretical option. Effectively it locks down combat to one weapon set and makes the other(s) superfluous, which takes away strategic choices and, well, fun!
My thoughts on possible solutions (the bit you probably won't care much about)
The "easy fix" would be making it a free action - but on its own that would open it up to shield exploitation.
However, I think the template "Major, Minor, Move, Free" would work very well in this game. It's almost there, but minor is missing which is the crux of the matter.
Minor actions would add a few advantages mechanically: There are some buff spells that could be minor instead of free, to limit how many you can get going in a single turn, and some current standard spells that don't get used could be minor to make them more attractive... and it would make it possible to have a weapon swap without burning your standard action.
An alternative, if minor actions is too large an overhaul, would be to make free weapon swaps once per turn class features for melee classes.
If that's still not limiting enough, you can add restrictions such as "twice per combat", cooldown or "can only swap weapons as the first action" (to avoid shield exploitation) etc.
To be clear: I love what you've done with the game - I just feel it could use a few adjustments here and there
Adding turn based pushed PoE2 the last nudge up to GOTY 2018 for me.