Personally I like random generation, but it requires right place/genre. And most exiting results going from mix of handcrafted prefabs/rooms and generation...
You wondering earlier about LAB popularity, I can't talk for others, but I think it's consequence of cozy retro levels, satisfying weapon difficulty balance and good level partitioning.
When I looks at ZM screenshots, I feel like returns many years back, to HL with my first own PC. It feeling when you exiting about new unique weapons and try to figure-out new ways of interaction with environment.
I tried mapping myself many times. I love it as process, even when no one playing my maps include me. But mostly I miss something to finish it, sometimes just environment features to implement my thoughts or more sens to polish (when no one plays). I tried to write my own games to gain full control of gameplay and fill the gaps, but I was lack of patience, and just can't enjoy it enough time, to build something really-cool before inspiration was burned-out.
I think You already was done notable part of game to get fun as player, and have a wide control with custom engine, and may be just can have fun from mapping process itself... Yes, told man who can't really finish no one game even at jams.