ADOM is one of the best of the rogue-like games.
ADOM is a great game because it takes all of the things I liked about Nethack: the items, fights, and character building, and does Nethack one better by adding a real story and more interesting quests. Character development is well done, without the useless challenge classes like Nethack's Tourist. The weapon skills system is the best strength of the character development as it lets you develop proficiency in the weapons you use rather than just gaining abilities with character levels. Magic is generally a lot of fun to use and can be used by everyone (unless you don't know how to read) so you can have that fighter that casts the occasional spell when he really needs it.
The settings of the game are varied enough so that you really have an incentive to explore instead of every level being randomly generated. Some of the unique environments are a lot of fun to explore and are quite a challenge.
ADOM shares the problems of all rogue-like games: lack of a real save game feature and too much dependence on random encounters. I am an experienced player and I have never been able to get past level 15 (which is only about 1/4 of the way through the game or less) without "cheating" by backing up my character so I could restore if I got into a particularly nasty random encounter.
The randomness also can start your character off at a huge disadvantage -- especially if you are a wizard and you get a bad selection of spells at the beginning of the game.
There are also a few quests that can get very irritating because they ask you to retrieve items that can only be found randomly in the game (and they are rare too). So if you want to try for one of the harder endings, it can be nearly impossible even if you do use character backups.
The Bottom Line
ADOM is a rogue-like RPG that puts you in the role of a wandering Hero that is called upon to investigate the source of the corrupting evil in the Drakalor Chain. You will travel through many locations, from the wilderness to the darkest caverns to discover the source of the corruption. If you aren't careful, you may succumb to the corruption and become a servant of chaos yourself.
ADOM allows you to make a wide variety of characters and develop them in many ways, due to the unique skills and level-based abilities that you can develop and the many strange and wonderful items you find along the way. It is superior to most other rogue-like games because it is not just another random dungeon crawl.