I'm sure that some of these suggestions will be fairly contentious, however, I beat the game on PotD using only story NPCs, didn't use figurines/potions/scrolls/traps, had expert mode on, and found it to be more of a 'hard' mode (hard mode was much too easy) than a ridiculous, unfair challenge. I even ended up using Cheat Engine to drastically reduce my party's experience on multiple occasions. If they're too much for expert mode/PotD, maybe they could be implemented, with others, into an even higher difficulty mode for the expansion/sequel, 'Way of the Grognard'?
-Only one figurine should be capable of being used at a time (maybe even only one total per battle), not one per character. When every PC can use a figurine simultaneously and some figurines summon multiple creatures, it's equivalent to an instant win button (to a game-breakingly absurd extent in the early/mid game) that completely trivializes any fight in the game.
-Characters should be granted a brief period where they have an increased resistance to whatever hostile effect just ended. When currently afflicted with a hostile effect, characters should also have an increased resistance—perhaps even total immunity—to that same effect. The capability to effortlessly resolve a significant percentage of the combat in the game by simply stun-locking enemies indefinitely at a choke point using mental binding (a 2nd level spell!), and with only one cipher in the party to boot, is ridiculous.
-The total absence of immunities leads to numerous preposterous in-game scenarios. For example, blights (elementals) take damage from their respective elements; they shouldn't just have a total immunity, they should actually be healed by attacks featuring their respective elements. Oozes can be knocked prone. How do you knock a gelatinous mass on its back... where is its back for that matter? Spectral enemies that hover above the ground can slip on a 'slick, oil-like substance' that 'coats the ground'. Flying enemies are also vulnerable to being knocked down by an oily, ground-based attack. Enemies without eyes can be blinded... clearly wizards are some sort of inverse-Jesus. This a wide-ranging problem that contributes to the bland uniformity that defines much of the combat and is in no way limited to the handful of examples listed above.
-Figurines should be single use items, not one use per rest. A few more figurines could be introduced into the world to compensate for this. It would be even more interesting if some figurines summoned hostile creatures or ones that turned on the summoner once the enemies were slain. Hell, there could even be one that summoned a creature/person that gave a quest to slay the person who imprisoned them in the figurine.
-Enemy humanoids should use potions/scrolls/figurines and intelligent (sentient beings) ranged/spell casting enemies should ruthlessly target the player's casters/squishies, forcing the player to disable them or immediately burst them down.
-If PCs can have, at a minimum, two weapon sets, why can't other humanoids? If enemies were given alternative methods to attack—be it ranged or melee with extended reach—the common indoor tactic of blocking a doorway with your tank becomes a lot less OP and makes for far more interesting and dynamic encounters. The engagement tanking cluster**** that most fights occurring in the open devolve into would also be mitigated to a large extent by such a change. Of course, this is contingent upon a semi-decent AI being implemented into the game.
-Failing a scripted interaction's option should always have some contextual punishment, on many occasions actions were attempted and failed, yet no ill effects resulted from those failures. For example, if a character attempts to climb up to a window via vines—instead of immediately using a grappling hook—and fails, falling to the ground in the process, they should have a twisted ankle debuff (or something similar) until they rest. If a character attempts to push some rocks out of the way—instead of immediately using a hammer and chisel—but isn't strong enough, they should get a sprained back debuff or something similar.
-Bounty experience should be 1/5 of what it currently is... if not less. Side quests in general seem to grant too much experience. This seems to be a problem inherent in the amount of experience required to level up... the curve is much too gentle from around level 3 onward. It honestly feels like there is enough experience in this game to level two full parties.
-Bestiary grants too much experience, as the player is over leveled quite quickly after reaching the first major city without even doing a certain keep or exploring a certain multilevel dungeon. It really seems like the side quest exp wasn't reduced once the bestiary exp was tacked on at the end of development. At the very least, expert mode and/or PotD should reduce—if not remove—bestiary experience. Another possible solution is to offer bestiary experience only for enemy archetypes instead of every individual variant of said archetype.
-Chests/traps shouldn't grant experience. The reward for opening a chest is whatever is inside of it; the reward for disarming a trap is the removal of a dangerous obstacle. Reclaiming traps should be a 50% chance at the same level of mechanics and +/-10% per level above or below.
-The endurance regenerated after a battle should be taken from the health of that character, with the caveat that the total health couldn't go below 1hp. This would make the 2 camping supply limit on PotD actually impactful. It would also make potion/scroll use important, if not necessary, in certain sections of the game.
-Swapping weapons shouldn't be instant; it's too easy when you can equip a caster with a hatchet and a large shield then just immediately switch to that set when anything gets within striking distance, gaining an immediate and significant bonus to deflection. When wizards have multiple spells that buff deflection and are not instantaneous, like switching weapon-sets is, it seems like weapon switching isn't working as intended. By making weapon switching take some time it also allows a talent to be introduced, making it faster, or even instantaneous, further diversifying meaningful build options.
*Mild Early Game Spoilers*
-An enemy should only be capable of being charmed once per encounter and should go hostile immediately upon taking damage from the player.
-Enemies shouldn't immediately attack their charmed allies if they have other available targets. Currently enemies will frequently immediately target—and even chase (eliciting engagement attacks in the process!)—a charmed ally of theirs, completely ignoring what or whomever they were just fighting.
-Resting bonuses should only last until the next rest, not until they are replaced by another bonus. I suspect this to be a bug since it occurs sporadically.
-Great sword needs to be buffed as choosing the estoc is currently a no-brainer.
-Enemies 'leashing' leads to some very exploitative scenarios and thus should be removed.
-Dunryd Psion hireling is garbage: 100cp per day and -2/+2... why would anyone hire it? Brutish Warrior is +3/+2 and 50cp per day for comparison.
*Mild Act 2 Spoiler*
-The 'Overbearing' enchantment should have its prone duration halved... a buffed (or even unbuffed) carnage barbarian with high intelligence is currently too powerful when using weapons with it.
-Pale Elf's Burn and Freeze DR should be reduced to +5 from +10.