Lets just assume that making sense is mandatory so we dont get a lot of Wayne/Eminem posts
i'd have to say Wordplay-metaphors, similies, puns, entendres. Should be first because aside from Flow this is the single most effective thing rappers do.Without it rappers dont distinguish themselves from just a randomn nigga talkin on beat or poets/speakers. the ability to use multiple english devices rapidly what keeps us sayin "__ is dope" This is what stands out the most and is the most noticable. This really seperates rappers into different classes when we have our debates. Bad punchlines/wordplay makes u cringe and can turn people off very quickly. Whereas clever wordplay will propel a rapper from his peers
2nd would be story telling. if you're not able to paint a picture with words and have people connect with what your saying or conveying, you're really putting a ceiling on how ill u can be considered. Just about every punchline rapper falls short in this category
3rd is rhyme schemes which is self explanatory. Do you sound the same on every song. Do you switch your flow up. Are u using the same patterns. Where do u drop ur punchlines. Do u connect metaphors throughout the verse/song.
i dont put too much emphasis on vocab the actual words arent as important as the content/context and the delievery. a rapper like Krit has simple vocab that covers a wide range of topics and emotions. Just because you're cramming 10 letter words inbetween every bar doesnt make u iller than the next nigga who just said what u did in 3 bars