I've seen the underground house tours on HGTV. They didn't seem too dark. Many of the houses have a wall of angled windows on the "open" side or skylights.
I've also noticed when I visit many homes that people in regular "above ground" houses often have heavy drapes and blinds closed over their windows. They purposely keep their houses dark inside. (I don't like it that way but that's their preference.) They don't even use their windows, so sometimes the lack of light isn't an issue for some people.
I guess the moisture situation depends on the building materials used, the local geology, and local humidity. Some areas have high water tables, some have sandy soil, some are granite, some are clay, etc.
In the South Carolina Lowcountry, we can't even have basements because the water table is too high. There are no underground houses here. But in other places, underground houses make good sense.
I recently saw on TV a house that was made from an old underground missile silo. It was truly "underground", several stories down. But they made it very livable and cozy.
Remodeling : Deep in the Ground of Texas : Home & Garden Television
Atlas Missile Tours
I think it depends on the person. Some people feel cozy and secure when they are enclosed. It's not for me. I like to look out, and have lots of bright sunshine in my house (even if it does fade fabrics, ha, ha).
So, some of the pros and cons depend on personal preferences.