He makes good music? More specifically: I like introspective lyricism. Rappers/singers who are able to paint a vivid, emotional picture of not only their own state of mind but show the ability to do it for other people/places as well. Nas comes to mind. Common comes to mind. And Kendrick does too. That "project window" perspective.
I also like narrative and storytelling, which is why Ghostface is in my top 5. Kendrick tells dope stories and understands that doing so has nothing to do with a "this happened and then this happened" framework. Like Ghostface, he creates a world and lets you step in it as he tells the tale. That's something most rappers don't understand, IMO.
GKMC is an amazing concept record with multiple highs, from bangers to shyt like Sing About Me. Speaking of which, that song encompasses everything that makes Kendrick a dope rapper in terms of the introspection and differing perspectives presented.
Am I gonna say Kendrick is one of the greatest rappers of all time, better than Nas etc like Peter Rosenberg's dikkriding ass? Hell no. But he's dope and nobody is coming close to his catalog right now, with Danny Brown, Vince Staples, and Billy Woods being the closest competition. And maybe Gibbs.