Lol he is Kenpachi. Backstory: Rogue warrior, renegade, fighting for fun.
Even now his appearance is all roughed up even when he isn't in a battle.
What did you expect his shikai to be? A pretty flower like Yumichika? Some beautiful pink display of small blades like Byakuya's? He's Kenpachi, of course he will get an appropriately ugly weapon to fit his personality. And it's not bad, it's appropriate.
Now Kenpachi should either quickly finish Gremmy off ...
Or else, I won't be surprised if he goes trollface, and creates a third clone and spams meteors.
And Gremmy ain't kidding about his power since even the SR were showing signs of panic at that attack.