The new character designs was lazy
The first Ralph movie has great memorable original characters, like Fix-It-Felix, Sarge Calhoun, Turbo / King Candy... even the police donuts and the sour candy were fun and interesting designs.
The sequels only has a bunch of generic designs. Except Eboy, he's good. The racing gang were the worst. Their designs were all very bland and uninspired.
You see, Candy Rush was a clever mash up of Mario Kart and Candy Crush. Both are hugely popular games in real life. But in the movie it's even better. It's pretty, and it's iconic. It's the "Wreck-It-Ralph racing game" everyone knows.
Slaughter Race, however, doesn't have any clever twist at all. It's not the "Ralph Breaks the Internet racing game", it's just a regular ass game found aplenty in real life. A mediocre one at that too. It has no creativity whatsoever.
Yesss was just too random. Even her name is random. Yes with three "s"es? What. What? Why? KnowsMore and Spamley look like rejected emotion concepts from Inside Out.
Fortunately, the Disney princesses saved the day.