Seriously, you click this link, you download this game, and I'm just not responsible for what happens afterwards. This game is rather addictive.
Desktop Dungeons is a hyper-compressed roguelike. A lot of other dungeon RPGs in the genre are fairly long games with permanent death, and as such players' first reaction to this genre is disgust with the idea of dying permanently and losing all their stuff. Desktop Dungeons sidesteps this problem by being ten minutes long: the game might be best described as dungeon crawling meeting Minesweeper. Perhaps the problem wasn't that games like this are too small, but that they weren't small enough?
The dungeon is but one screen, randomly generated. Monsters are stationary, and they don't attack unless you attack them first. If you mouse over any of these guys you get full details, as well as an estimate of what will happen when you do attack (the bright red DEATH indicator should keep you from clicking the wrong guy!). The classes have their weaknesses and strengths against certain types, so you want to be careful of this stuff. On top of managing your resources, a lot of the strategy of this game comes from killing the right monster at the right time.
You start out in darkness and have to reveal the rest of the dungeon by walking out into it. Now here's one of the big hooks of the game: in most roguelikes the player can recover life and magic by simply resting for a few turns. In Desktop Dungeons, the only way to heal up is to venture into unexplored sections of dungeon. As a result, the crawl is very calculated and it's actually a waste of resources to run through the place as fast as you can: you really don't want to go exploring too far unless you're at least a little beat up.
Given the nature of the game, not every dungeon is winnable. Many are, though, and as you get better at playing the game you'll learn a lot of tricks that will help you out in subsequent visits to the dungeon. As you win with each of the various classes, the game unlocks even more content that leaks into the games in further plays. There are also some unlocks hidden behind very specific and very cruel challenges, if you want to really get nuts.
The next post will be introductory strategy, I guess!