Hello, I'm new here, so I figured I'd introduce myself by selling you on Aquelarre (https://www.chaosium.com/aquelarre/). There are other reviews out there that cover the basics, so this review will just highlight what is different and interesting about this game, in terms of having run and played it. My group has played it over several sessions now, so we have the basics down. We are probably doing many things wrong but we are having a tremendous amount of fun with it.
Strange but Familiar
Aquelarre is set in 14-15th century medieval Spain, though Spain was not a thing then, so it's the Iberian Peninsula. This is the late middle ages. All PCs are human, which lowers the learning curve as you don't need to worry about different races. However, magic and miracles are real, as generally believed by real people in the setting, so you do definitely need to worry about the supernatural. So, the setting is immediately accessible while also being very rich. The familiarity grounds the game. Players know when they witness something supernatural because it would be the same as in today's world. Compare with other fantasy games, where running into a goblin may or may not be an astonishing event; the player has to be well-versed in the setting to know how the PC should react. In Aquelarre, the players immediately known when shit gets weird, and this is quite refreshing.
Good vs Evil
So as you can probably guess, there is a lot about God and the Devil in Aquelarre. This is how medieval people thought. This creates an underlying tension between Good and Evil that pervades the game. As the GM, this is really useful to create conflict and opportunities for adventure. Since the GM knows how the PCs are aligned, you know to hook them into a quest. For example, if the PCs are Good, then have a priest ask them for a favor. If the PCs are Evil, then hook them with a chance to learn forbidden knowledge.
Good vs Evil is a simplification, in game it's Rationality vs Irrationality. Being rational means believing in God and science (Good). Being irrational means believing in demons and other supernatural beings (Evil). A PC becomes more irrational by witnessing spells being cast and by encountering supernatural creatures. Conversely, a PC becomes more rational by slaying irrational creatures, resisting spells, and though Rituals of Faith.
In game play, the players' Rationality vs Irrationality scores can motivate their actions. Casting spells successfully and at higher levels needs high Irrationality. So if you're a witch or mage and your party keeps slaying irrational creatures, you have to try to do witchy or magey things to counter the loss of Irrationality. It makes for some interesting dynamics in play. We have a witch who is in this situation right now and so the player has her seeking out irrational creatures and other magic users to try to raise her Irrationality. We don't have a PC who is a member of the clergy, but it would work the same in an opposite sense with Rationality. He would need to take rational actions to keep his Rationality high to continue to function as a priest, monk, or whatever.
And the real interesting thing in play is that Good (Rationality) and Evil (Irrationality) are not the same as lower-case good and evil. This makes for interesting moral dilemmas, conflicts, and play styles. Our witch would be considered Evil if anyone found her out, but she takes time to help random NPCs, such as freeing a suffering man from the stocks. Similarly, our most Rational PC is a bit of a prick who tends to lie and steal.
Social Status
This plays a big role in the game. When creating a random character, you are more likely to roll a peasant or commoner than a noble. And, guess what, swords are status symbols, so you won't be carrying one around unless you are noble or unless you keep it hidden.
In play, status helps create interesting situations. A noble is likely going to trust someone of the merchant class over a commoner. Our mostly merchant party ran into some legal troubles and avoided it in large part due to the accuser being a peasant. They also got to bang around a village a little roughly because of their class. Now they are headed to a city where things are more complicated, and so are bound to run into bigger trouble.
Status is a great motivator in game. As GM, I got the PCs to take a quest just by having the quest giver (a lower noble) promise to put in a good word to the Duke. That's it! No reward more than a word.
Combat
The combat system at first read and during the first fight seemed crunchy and slow. Now that we have experience with it, it's a delight and quite quick. Let me explain.
Damage is high and armor takes time to don. Plus, you don't normally walk around in your armor now do you? A regular old hatchet can do 1d6+1d4 damage welded by someone with a bit of muscle against an opponent who might have 15 HP. Lose half your HP and your combat skills drop. Lose half your HP with a single blow and you can be crippled or killed. So a PC can typically take 1 to 3 hits before things get ugly. Have time to put on your armor, if you can even afford it, great! Things get a bit better, but not much unless you're in plate against a bandit in leather. So, there aren't that many rounds to the typical fight. We've been averaging 2-3 rounds.
Now for the crunchy bits. Initiative is rolled each round and you declare actions (strike, parry, dodge, etc.) in reverse initiative order before the declared actions are carried out. Some defensive actions, like parry, can interrupt. Bah you say, I want my combat rapid-fire rolls against target AC. Well, you are wrong! The declaration phase allows faster combatants to shape the flight. It also allows PCs to plan and cooperate around their strengths, something that would be intuitive in real combat but is not modeled well in other systems. You can win a fight with brutal efficiency by considering your declarations carefully. And something that was totally unexpected is that the declaration phase paints a clear picture of what's happening. Two of the players have literally stated "I can actually tell what's going on" during combat (compared to simple roll vs. target AC that we normally play).
We have found that fewer rounds and more thought in each round makes the fight more exciting and more memorable. Every action and roll counts.
Magic
As for Irrational magic, there are 200+ spells in the core rules. Some obviously useful and others really fucking weird. Do I want to be able to light a fire with some salamander blood? Yes. Do I want to eliminate the pains of childbirth from someone? Sure, I guess, but...that's crazy situational.
The spells have such a huge range, so that magic is much more likely to be used outside combat. For example, during the legal troubles, our witch used a spell to make the key witness stupid, so that he couldn't even remember meeting the PCs and therefore his testimony was useless. That spell by the way required the witch to feed the guy human flesh that had been marinated in ox blood.
Which takes us to the topic of spell components. Spell casters need to source these. Some are just local herbs but others are really hard to find. This makes magic exciting when it all comes together. It also creates opportunities for adventure. How do you think the witch got the human flesh? If you guessed she convince the rest of the PCs to help dig up a recently buried corpse, you are correct.
Rational magic, aka Rituals of Faith, is what the ordained clergy uses. We have yet to try those out, but they are less driven by components and more by ritual. Plus, the PC that performs the ritual needs to have a high degree of Rationality to succeed, with possible grave consequences for asking too much from God.
One last point is that any PC can use spells or rituals of faith. They need to acquire the correct skills (magical knowledge and theology) and in the case of Rituals, they need to be ordained, all of which can happen in game.
Summary
That's all I can write at the moment. Aquelarre is a rich game that is lots of fun to play. Feel free to ask me any questions an I will try to answer them. Cheers!