I'll use CK2 as an example, in my opinion:
Good DLC - Rajas of India (tons and tons of content just added on top of the game), Sunset Invasion (completely optional and not necessary), music (again, optional)
Bad DLC - Republics (can't play as anything but feudal by default), unit visual packs (they are literally simple models, no need to slap a price tag on them) etc.
That is odd to me, since RoI have been one of the most useless dlcs for me and Sunset invasion is the only expansion I haven't bought (it's silly)
I loved republics.
But that touches on the last point.
Units and portrait packs are not expansions.
I don't feel like sunset invasion was either.
If you have a problem with paradox charging for things that someone have been paid to make...
Not sure what to tell you.
I get the same attitude from people when I spend an hour finding an error in their network and they are suprised they have to pay me for that hour AND that I will charge them to fix it too.
Might I ask what you do for a living?
Or is everything you do free?
(Wait, don't tell me, you are out of work and getting paid or studying and getting paid for that too?)