I recommend this game with a bit of a warning. It can be fun, but only if you're extremely patient and don't mind having your ♥♥♥ handed to you every ten minutes or less.
It's a simple enough premise. Choose your mission. Choose your character. Go through the dungeon floors to try and complete your mission. Die. Try again. It's your typical roguelike in that regard. However, there is one thing that really makes this game more difficult than other roguelike dungeon crawlers such as Legend of Dungeon or even The Binding of Isaac (I know it's a bit of an odd comparison). The hit rate system in this game is seriously flawed. Your hit rate automatically starts out at roughly 60% regardless of what character you start with. You can deal a fair amount of damage and kill enemies in one hit, which is nice. Yet, you only hit them a fraction of the time and you can find yourself exchanging blows with a single enemy for two or three minutes until one of you dies. If you're surrounded by multiple enemies, odds are, you're going to die because you have such a small chance of killing them all before they've managed to kill you.
Luck based elements in roguelike games are not unheard of. Quite the opposite. They're a crucial part of the genre. However, when it becomes TOO luck based, it becomes a problem. Random level, enemy and item generation is a good idea. Random hit rates however are not. It makes completing a single floor almost impossible, let alone a whole mission. If you're patient enough to actually sit through countless runs of this game to beat a mission, then this is the game for you. However, if you do not like the idea of huge maps with a flawed probability driven combat system, then I would recommend other roguelike titles first.