From the very start, you can see where Book of Demons draws its main inspiration from, and really that's the entire point. Presented by developers Thing Trunk as "the first installment of...a series of original mid-core titles, inspired by the early golden days of PC gaming"; it is clear from its basic mechanics and look that Book of Demons is meant to evoke that classic Diablo feel (albeit with much more humor and cutesy paper cutouts).
Similarities begin with the classes you can choose. As the game is still in Early Access, the only two classes currently playable are the Warrior and the Mage, with the Rogue being a future option. They mirror the three classes from the original Diablo, and once you've selected your class (this preview is based on my Warrior playthrough), the similarities continue as you are introduced to the paper town from where you will begin your monster-eradicating crusade.
The very first thing you notice are the familiar red and blue Health and Mana orbs, complete with the devil and angel motifs. You meet a variety of townspeople who give you great narrated monologues about the state of their town, and how they can help you on your journey. These can stretch a bit long on occasion, but do give a surprising amount of characterization and personality to otherwise generic NPCs.
As it happens, the town was built over a hellmouth, and the town's resident Pope (turned Antipope) performed a dark ritual that opened the way for the Archdemon and his hordes. The townspeople now need a brave adventurer to go below the church and stop the Archdemon before he reaches the surface. You also meet your very own papercraft Deckard Cain, called the Sage, who speaks with the same shlight Shcottish accent, and also performs the important function of identifying cards.
The card and deck-building system is one of the unique aspects of Book of Demons. Cards are both your skills and your equipment, with only the cards in your card slots (located between your Health and Mana) being active. Loot in the game comes in the form of these cards, and any new cards require the Sage to first identify them before you are able to use them. At first you will only have three open card slots, but you can pay the Sage for additional slots.
You do not actually have any traditional stats like Strength or Endurance to manage. Leveling up in Book of Demons is instead simplified down to choosing whether to add to your Health or Mana pools. I found that adding to the Mana pool was clearly the better choice as both your equipment and spell/skill cards all rely on it. When you use equipment cards need, some Mana is reserved while they are active and will appear as green Mana in the orb. You will only have the blue Mana portion to cast any spell/skill cards, thus having a large Mana pool is a must.
Upgrading cards require the spending of expendable Rune cards, which can also be received as loot. This is where the bulk of strategy in Book of Demons comes from, as upgrades to skills/spells and equipment can be game-changing and even essential. These upgrades range from straightforward offensive/defensive power boosts, allowing you to ignore certain attacks, or deal super-effective damage to certain enemies. These upgrades are balanced by both the Rune card cost to upgrade, as well as the increase in Mana requirements that the upgraded cards use.
During combat, you're not just limited to the cards you currently have equipped. Bringing up the card inventory during combat will slow down time, and allow you to hot swap different cards into your active set. This allows you to tactically change your card loadout at any time, reacting to what enemies you're facing, or even to quickly use a health potion before swapping back to your weapon.
There is even friendly fire during combat, as your own spells or weapon effects can hurt you. This lends more strategic depth as you can make specific 'deck sets' that help offset this kind of weakness. For example, an Axe card that spawns pools of fire is enhanced by also using a Boots card upgraded to prevent fire damage.
When you first dive into the depths, you will be presented with another one of Book of Demons unique features - the Flexiscope dungeon system. It allows you to choose the length of each new dungeon session. This means a short two level dungeon that takes you about 8-10 min to complete, can become a sprawling eight level dungeon that takes the better part of an hour.
The bigger the dungeon you choose, the higher the amount of potential loot cards and gold you can find. Of course, with a longer dungeon length, you might find that you will not be able to complete it in one go. This is not a problem, as Book of Demons is very forgiving in terms of letting the player put down the game at any time, and returning to it later. You can save and exit a session at any time mid-dungeon, even during a boss fight, and come back later to the exact moment you left.
While the card system is tactical and the Flexiscope system is convenient, I was surprised at Book of Demons' take on hack-and-slash combat. Compared to other games in the genre, it's surprising how limited movement is. Your character can only move along a linear path throughout the dungeon. Players cannot get off the path and can only move forwards and backward along it, but enemies can freely move around you. In addition, all combat is ranged, as your auto-attacks reach enemies and items a very far distance away. This is the same even for the Warrior class. You will never need to physically go near an enemy to hit it.
Throughout the entire game, I was playing keep away with enemies as a Warrior instead of fighting them in close quarters. Fighting at range is optimal, as being surrounded by enemies at close-range is a death sentence since they can body block your only means of escape along the path. With the Charge skill card, I used it to get away from enemies instead of charging in. I was constantly spamming my powerful upgraded ranged skill card because it was efficient and safe. The truth is, I wasn't playing like a Warrior, but more like a really buff Mage.
The biggest disappointment for me though, was that none of your equipment cards are reflected on your character. Your character looks exactly the same no matter which weapon or armor equipment cards you are using. Even when you don't have a Shield card equipped, the character model carries a shield. The only visual change that happens is when your character reaches a level threshold, but it is a set of generic gray armor.
Part of the fun of Diablo-style hack-and-slash games is in seeing what loot you get and how they look on your character. Take that away, and you don't really have any motivation to keep going. None of the effort I put in feels rewarded or showcased on my character. This made my victory over the Archdemon feel very anticlimactic, because he did not drop any new or unique loot, just Rune cards. I had nothing to show for all my efforts.
Book of Demons presents itself as a tribute and parody of Diablo, and I think that sets up a lot of expectations that it isn't really trying to fulfill. I did not expect or want a clone of Diablo, but I did expect a game that would highlight the best parts of the hack-and-slash genre, and sadly it simply does not have them.
What is here is unique and polished. The cutout visuals are whimsical and somehow maintain a lot of detail despite simple looking designs. The soundtrack felt like it could have come from some lost level of Diablo or Diablo II. All the features it brings to the table in the form of the card system and the Flexiscope system work very well to innovate the genre. Book of Demons manages to present itself as a homage while still possessing its own distinct style.
However, once you have had the majority of the card drops in your inventory, nothing drops for you except for the expendable Rune cards for further upgrades. With no random loot generator of some kind, or having the satisfaction of viewing equipment on my character, I simply saw no reason to continue playing the game. They added the Mage character last month, but I honestly do not see how he would play any differently from my already ranged Warrior. It should be noted that, as the game is in Early Access, more content in terms of loot variety could possibly come. Still, I would not recommend Book of Demons as it stands, as it wouldn't please those expecting a traditional hack-and-slash or players looking for a lot of replayability.