Reasons that ADOM is better than
Nethack:
1. Its inventory system. God bless you, Thomas Biskup, for ADOM's inventory. Whereas Nethack assigns each item you pick up a key to press whenever you input a command (for instance, you would say, "Put on 'p,'" having to have memorized which one "p" is beforehand) ADOM gives you a very nice inventory screen, which you can scroll and everything, which lists all your items by category PLUS gives pertinent stats about the items (something Nethack doesn't do at all).
2. Its character gen. ADOM gives you ten races and twenty classes to mix and match, plus a randomly assigned star sign, all of which affect the character, not to mention gender. Nethack's choice is paltry by comparison.
3. The size of its gameworld. ADOM has tons of different dungeons, each with different themes and quests, plus towns and wilderness. The dungeons themselves are also huge, and, in some cases, infinite. Nice.