Knights of Pen and Paper is a fantasy RPG, which plays like tabletop RPGs. The twist is that you're playing as both the dungeon master and the players. Basically that means you can decide yourself what kind of quests you want (to some extent) and how difficult you want to make the fights by choosing how many enemies you want to fight against. And because the game is like tabletop RPGs, there are several situations where you'll throw a virtual D20 dice.
When you first start the game you get to choose from about 10 characters to be the players and 5 classes for them. Each character has a different passive bonus that increases some attributes, which actually leads to choosing the characters based on the bonuses and the class you're going to pick. When starting a new game you get to choose 2 players for free and the remaining 3 seats in the table you can fill by buying the players with in-game gold. You can swap the players in places that have a tavern.
If I remember correctly, you first have 5 classes available, but you can unlock a few more by completing side-quests. You can only have one of each class, so for example you can't have 5 warriors as your party. You wouldn't want to either. The reason being that each class has its purpose. Some classes are healers, some are tanks and the rest are either melee fighters or spellcasters of some description. Each class has 4 skills, which are either passive or spells and skills that you can use during combat. The passive skills usually boost some attribute, but some of them also have special stat boosts like life steal. The active skills are pretty basic fantasy RPG skills. You can increase one of the skills every time you level up, which just made the skills more powerful or increased the attribute bonus. So it isn't very deep skill system.
The combat is turn based and the players and the enemies all have a box either on top of or below the sprite, which shows the number of their turn. On the player's turns you choose to either attack, use a skill/spell, use an item, defend or run away from the battle. You quite rarely want to use anything other than a skill or spell, because those are the most effective way for beating the enemies. As I mentioned earlier, you get to choose how many and what kind of enemies you want to fight against. Once you buy a certain item from a special shop you can fight 7 enemies at a time, but before that the maximum was 5, I think. I bought that item very early on and didn't check the maximum amount before that. The enemies you can choose from vary quite a lot and you can often choose to fight tougher elite monsters, which give better rewards.
I thought the combat was quite fun, but it got kinda boring after 8 hours because in the end it was just the same thing over and over again. At least they kept things fresh with different enemies. The difficulty ramped up quite a lot after about halfway into the game, when the enemies suddenly became very high-leveled compared to the players. Surprisingly enough, I could survive against much higher level enemies than my players were provided I only fought against 3 at a time. It could take a long time to kill them all, but I still could do it. I suppose I played it quite safe since most of the time I fought battles I knew I could win and as a result my whole party died only 3 times during the time I played the game.
When you're not in combat you can choose from several options depending on your location in the world. In almost every place you can choose to rest, start a quest specific to the location, use items, check the equipment of the players or travel to some other place. Cities usually also have shops for buying potions and equipment, a tavern and a blacksmith. The blacksmith can upgrade your equipment, but you shouldn't do that until you have increased the blacksmith's level enough for the odds to be on your side. The upgrading is chance based and it happens by throwing the dice. The range of "winning" numbers increases as the blacksmith levels up, which makes it easier to win. It's also a good idea to have level 16 players, because then you can equip items that decrease the equipment upgrading cost. I wasted several hundreds of in-game gold before I found about those items.
Moving in the world happens by opening the world map and then choosing the location. Traveling costs some gold and every time you move on the map, you throw the D20 dice and depending the roll you might get a random battle. That would get annoying very quickly, if you had to fight some low level monsters when moving around the starting area with high level players, but luckily the chance for the random battle depends on the players' levels and the levels of the monsters in the area you're travelling to. You can also a buy an item that permanently increases your dice rolls by 1, which makes it impossible to get random battles in low level areas. I thought the time it took to travel between each place was a bit too long, but you could reduce that to half if you had a certain game master active.
Quests were quite repetitive and not very fun. There is basically 3 types of quest: kill x amount of certain monsters, escort/deliver something and "fetch" some items by going to a certain place and killing the enemies there for the items and then return to the place where you started the quest. On the upside the quests gave a lot of experience. There were also some story quests as this game has a (boring) story about saving the pen and paper world. I think the dialog should have been funny, but I didn't find it funny. There were quite many references, but those weren't funny either. At one point I stopped caring about the story entirely and just skipped through the dialog. I just didn't find it interesting at all.
The game also has a special store that you can access anytime you're not in combat or in the middle of some conversation. The store has items like furniture, which boost something permanently, and snacks, which give a boost that only lasts for about 15 minutes. You can switch between the furniture you have bought without having to buy them again. I usually switched them based on the situation I was in. Everything bought in this store transferred to other saves too, so you only had to buy the stuff once.
I believe the game was originally designed for phones and tablets as there is an in-game store, from which you can buy in-game gold for real money. However, using the in-game store is never required and it can be completely ignored. Once you reach a certain point in the game, you can easily get around 300 gold from a fight that lasts for a minute. The in-game gold is transferred between saves so you can have a save for farming gold for the other save. The real money store in the game seems to be a thing that makes some people skip the game entirely, even though you never have to use the store.
The graphics are 2D pixel art and the sounds effects are pretty old-school bleeps and bloops. There is no voice acting, so you have to read through all the dialog. I thought the music was repetitive so I ended up muting it.
Overall I thought it was pretty enjoyable game and I was quite addicted to it for a while. I played it for 21 hours in total, which included me first going through half the game and then starting a new save to get couple of achievements. I finished the story in the second game I started and also beat the optional boss. I also got every achievement aside from the 3 broken ones. The boring story and the in-game real money store are definite cons, but the rest of the game is fun even without very deep character development or combat.