I like Angband. It's easier than Nethack imo. You don't need to know anything about LOTR to be able to enjoy it. In Angband, Every level (minus the town) is randomly generated but levels don't persist, meaning you will always get a new level when you go up/down. I recommend you read the official docs: https://angband.readthedocs.io/en/latest/index.html
(or watch a walkthrough)
In the character creating screen, you can press = to change some settings. I recommend that you make everything sell for 0 gold because the game will then generate more valuable gold drops and you don't need to go to the town so often. There are also other options but you don't need to change them.
Other games worth trying:
* Nethack/Slash 'Em/UnNetHack/Vulture's Eye (isometric gfx)
* Elona+
* Demon (A Monster Collection Roguelike)
* DoomRL (easy for beginners)
* TOME4
* Cataclysm: Dark Days Ahead
* Dungeon Crawl Stone Soup
* Dwarf Fortress (adventure mode?), I recommend getting tileset or using LinuxDwarfPack.