Xin is an amazing laner in certain situations. I love dominating duo-lane with my buddy playing as Taric, where we play as bush-*****s and he initiates with his stun, I jump with and knock the enemy up, as we merrily beat him down for the entire lane phase. If we get someone stupid enough to push rather than last hit, our kills just shoot up ridiculously.
Then there is the downside, where Xin fights against a ranged DPS, a support or a tank without a good lane partner. I have lost count of all the times where I've had to B and waste my Ghost after I've jumped an Ashe only to have her kite me like a boss and nearly kill me. Same can be said for a Janna who shields herself then tornados me while he ally destroy me, or a tank with solid CC that locks me down.
When it comes to teamfights, unless Xin Zhao is at the frontlines he really can only target down one enemy. Sure his ultimate hits everything, but thats a one-time thing, and even then it doesn't increase his damage output to heavily.