Meld with the beat?
Most of the more popular rappers today are great at harmonizing with more "poppy" beats, and blending their flow with the beat. Some great examples are Gunna, Lil Uzi Vert, and Lil Baby. Trippie Redd is another one.
They're great at blending more melancholic topics (like depression, drug use, suicide, etc.) into hard-hitting songs, which is one of the reasons why the shyt that they say goes over so many heads. Juice, Mac Miller and Lil Peep all rapped about addiction and such, yet it still came as a surprise when they died.