How would you compare ADOM to other rougelikes? (Nethack, DCSS, Angbad, etc.)
It starts you off in an overworld and the initial progression is less linear than the traditional dungeon-delving approach of eg. Nethack and DCSS, so in that sense it feels more RPG-like.
I never really got into Nethack much because it's just so punishing, and while ADOM is definitely far from an easy game, it felt better. DCSS is also similar to ADOM in the sense that the development community tries really hard to make it an enjoyable experience.
Mechanically, it has moderate (though polished) depth. But it has more story and unique events than most roguelikes. It benefits far more than most from playing entirely unspoiled; there's enough information in-game to solve all its puzzles.
As far open sourcing the code is concerned, I remember the author said that it would open-up some secrets which players would otherwise will have to discover. E.g existence of "inn of the red rooster"
I've heard that argument, but people have figured out the various mysteries anyway through reverse engineering. I don't think anything would be lost by opening it up.