Pro Tons of character combinations
There are 7 races and 12 classes that are combinable as well as 4 extra monster classes that do not allow choosing of race making for 112 unique combinations, all with their own custom avatar. There are also 6 additional special races as well as 9 different gods you can worship during the game for even more abilities.
Pro Mix of puzzle and roguelike
The game gets its roots from roguelikes, and the complexity of the combined genre really enhances the puzzle solving side of the game.
Instead of being real time, or taking place in a large expansive world, Desktop Dungeons games take place on a small 20x20 dungeon. Although the map is small, there is tons of strategy to figuring out the optimal way to clear the dungeon. Unveiling tiles is how you recover health and mana, so the game is fundamentally about efficiently using the tools and resources available to you in each map and coming up with unique strategies in such a small space. You must balance the risk between trying to get experience from exposed monsters and exploring deeper into the fog of war.
Con Hidden map means you can't solve the puzzles on logic alone
The map is hidden by fog of war until you explore it, meaning you can't devise a solution from the start. Because revealing the map regenerates your health and mana you can't explore everything at the start. You need to spend most of the game not knowing the state of the rest of the map.