Endgame lacks depth and difficulty

I would like to see some serious and interesting end game content where progression is based on skill and not that much on gear.

However if there are multiple difficulties available for it (so everyone can experience it) the loot/reward should differ not in amount but strength/quality of the items.


Primarily I think about dungeons like the three at the basement of The Watch. However instead of one linear path there could be a more complex and interesting layout to explore with multiple bosses and events, doors to open, different options how to find your way through it (without the need to lay every boss, etc.). There could be some more interesting riddles opening up different pathes, maybe even in combination or against each other that aren't just simple memory or search yourself to death until you found every rune. It should be more about complex/critical thinking in an endgame scenario.
Questlines could also be part of those dungeons with NPCs and objects to interact with, maybe to rescue etc.

I have no idea if this helps, but I consider blackrock depths from World of Wacraft (Vanilla Classic) as a great example for a fun multiplayer dungeon experience for those who love to explore.