I personally think more enemy variety in the combat situations will go a long way. Right now it feel like most of the time you are fighting the very same type of enemy, just multiple of them.
In comparison, tougher battles in BGII always had you fighting agains a party of a tank, a DPS character, a cleric, a mage, a ranged marksman, etc. These situations seem much, much rarer in PoE and combat is often boring.