If I'm gonna put a Grime track on a mixtape for someone, it pretty much has to be JME. Most other Grime bars are just self-referencial/gun-chat = major turn off for a lot of people. JME's tunes are, for the most part, pretty much accessible to anyone.
Couple that with some killer beats and choice of beats, as Logan said, and you've got the perfect cross over artist.
Stuff like 96 Bars of Revenge, 96 Bars of JME and Boy Better Know sound good surrounded by whatever other music. It's grime you could hear on the radio. I really like that track Deceived from the Derkhead mixtape as well. Much better take on "comedy" Grime than Sway or whatever.
The whole Boy Better Know thing has just been a stroke of genius really. Nice strong image, good music, interesting little side-projects (BBK Fighter etc). Some of his catchphrases like "Serious" are already crossing over a fair bit. I'm pretty sure the kids shouting "serious" in Channel 4's Skins were directly referencing JME...