This game definitely has all the characteristics of a roguelike but is modernized in a way that let's us mere mortals enjoy it as well, has a great artstyle and enjoyable humor, and of course, extreme difficulty.
Your goal is to get through all ten floors and defeat the dreaded Lord Dredmor, but DLC adds an additional 5 floors as well as bonus floors. I would definitely recommend getting all dlc and the base game at the same time, especially considering the price for the amount of content.
If you're not daring enough to get through the entire game on its intended settings you can disable permadeath and/or lower the difficulty.
This game is also highly moddable, which should further extend the large amount of replayability that already exists in the base game, just look at the steam workshop for some fantastic user created mods.
And remember, dying is fun! Sometimes!