With all the story stuff out of the way, how does Inquisitor actually play most of the time? The unfortunate fact is that while the game can call Baldur's Gate, Diablo, Divine Divinity, and more its influences, it only takes from them superficially. Outside of the towns, Inquisitor has the large world map and overland exploration of Baldur's Gate, as well as the deep dungeons of Diablo and related titles. Unfortunately, it is all marred by the excruciatingly awful combat and some of the most pointlessly over-long dungeons I have ever seen in a game.
Combat makes up approximately 70-80% of the time you will spend with Inquisitor, and it is not good. It superficially resembles Diablo, or perhaps Lionheart or Arcanum's real-time mode - you click on monsters and hack and slash at them until they die (or cast spells, or shoot arrows as the case may be). Party members are available and pretty much indispensable, not so much for their damage output, but because they will absorb incoming damage from enemies and keep them distracted. On a basic level, it sounds alright.
Where it all falls apart is the "feel" of combat and game balance. Character movement can be very floaty and imprecise at times. Even though Inquisitor is a point-and-click game, characters will often "slide" and "bump" each other around, especially in close quarters, which can sometimes make targeting enemies frustrating or will lead to mis-clicks which send you running to your doom. Due to the size of battles, the visuals can also become very cluttered as you will routinely have 10 or more characters duking it out in close quarters, in which case it can be nearly impossible to tell what is actually going on.
But the real sin of Inquisitor's combat is game balance. I do not exaggerate when I say that have never, ever seen such a poorly balanced RPG, in everything from the character system, to enemy stats, to equipment and items, to the magic and spells available. To start, one of the reasons combat is so incredibly frustrating is that enemies have far, far too many hit points and resistances. On the normal difficulty, many enemies can individually take anywhere from 10 to 30 seconds to bring down, each. Combine that with the fact that often just about every dungeon room you visit will have 5 to 10 of these enemies in them, and then consider that the average dungeons might have 10 to 20 rooms all full of these numbers of monsters, and you can now start to see why this game is indeed "100+ hours long".
Inquisitor is also not a very challenging game, or at least, when it is challenging, it is rarely because of difficult encounter design or enemies with interesting spells that need to be countered, like some other classic RPGs. Rather, many enemies are loaded with extremely annoying abilities. Area-of-effect spells that damage and stun all your party, leaving them stun-locked with no effective counters? Check. Debilitating status effects that prevent you from regaining stamina? Check. Slows that make you attack at half speed? Check. None of these have any reliable resistance whatsoever, and the enemy AI ensures that they will spam these abilities constantly. The enemy AI itself is very primitive too, and they have no real behavior beyond "cast all spells until mana is depleted, then follow the player and keep attacking with primary weapon" which also adds to the repetition.
Instead of a puzzle to be figured out, combat is more like a grueling gauntlet. Inquisitor's challenge comes less from the gameplay mechanics and more from the simple question of "do you have potions?" If you do have potions, you will be able to constantly quaff them down and keep your health/stamina/mana levels up. If you do not, you will die, usually very quickly. Party members also like to consume potions far faster than they actually need to, and they always drink the best ones first, so you will likely have to micro-manage their potion-drinking habits. If you run out of them and don't have a Magical Box to summon a djinn and open a shop interface, usually your only choice is to slowly walk back to town and restock, wasting 10 to 20 minutes of your time in the process. It's surprising Ultherst doesn't have a potion-based economy, as they are basically the only items of value worth buying. Speaking of, equipment available tends to be pretty poorly balanced as well - you can buy the best items in the game even in the first act, and the stuff you find in the world, including unique artifacts, rarely competes with what you can get by re-rolling the shops around town, so there is almost no equipment progression once you have collected a decent amount of money.