20th Century Fox has a dose of great and well-known films and TV shows and many movie franchises. A dozen of examples:
Alien
Die Hard
King of the Hill
Family Guy
Futurama
Predator
Planet of the Apes
It's Always Sunny in Philadelphia
X-Men movies (e.g. Deadpool, Logan, Days of Future Past, etc) and TV series (e.g. Legion and The Gifted)
X-Files
Home Alone
Avatar
Titanic
Star Wars: A New Hope (distribution rights only)
MASH
24
Bob's Burger
Disney's acquisition of 20th Century Fox would change the entire entertainment industry in Hollywood and possibly put Disney's streaming service in direct competition of Netflix. It would give Disney an adult department and giving them the market in the adult animation department. On the other hand, it would increase Disney's monopoly over most of Hollywood and possibly threaten small businesses and independent-film makers, that's a negative.