Thank you for your generosity! I send a biiiig +1 your way! ;)
I'm in, and here's my answer:
For Avadon: What is The World's Best Roguelike?
This is a tough one, because Nethack and ADOM are both on my toplist. But because I have to choose, I say it's ADOM (Ancient Domains of Mystery).
The reason for this is:
1. It has a semi-random world, which means all it's locations are always on same places, but the contents of dungeons / etc. is randomly generated. That way, I can always head for specific dungeon, and when I get there, it still feels fresh.
2. Lots of choices for character builds. The game has a really robus character creation system, which let's you mix and match races / jobs freely. Want a troll wizard? Just do it!
3. Lots and lots and lots of looot! :)
4. Corruption system is unique, and it creates tension as your character slowly corrupts to a hideous monster! :O
5. The game is FREE!
I think, that I might have come up with more good reasons, but these are the main points for me. If you haven't tried ADOM yet, try now, it's FREE!!! :D