Skills
Passive
His passive both gives him a shield (60 at level 1, 650 at level 18) and doubles his crit chance. We'll talk more about the crit chance when we get to his recommended build. The shield is amazing. It charges while you run, the faster you run the faster you get charged. at level 18 he is granted a 650HP shield. If I wanted to get that on Vi, I'd have to get 6500 health. Don't underestimate this shield. If you keep moving and spam your E in teamfights, you'll probably proc this two or three times.
Q
W
Wind Wall will block enemy projectiles passing through the front of the wall (yes, it's directional). Useful against things from Nami's ult to tower shots. Max last.
E
Sweeping blade will allow you to dash towards a target. It's range is pretty small, about 475 units (5 Teemos). When you cast Q + E, his Q becomes a circular slash instead of a stab. With such a low cooldown you can leapfrog your way towards retreating enemies, but you have to be smart about prematurely jumping at your target. You won't be able to dash again for 6 seconds at max rank. Max second.
R
His ult will do 400 + (1.5 bonus AD) damage at max rank. It will hold all airborne enemies in the air for a little longer, however you will only deal damage to whoever you target. When you reach the ground, you will also have an additional 50% Bonus ArmPen, making it relatively easy to take down those pesky armor stacking tanks.
Recommended Build
His recommended build gives him a lot of attack speed and enough crit to reach 90% with his passive. On top of that, you'll have enough attack speed to completely disrupt an enemy team for the majority of a teamfight. He is pretty squishy, so I'm recommending you pick up some defensive items, as you'll be having to be in melee range to deal damage. Overall I'd follow most of the recommended items, but a Spirit Visage/Bloodthirster/Trinity Force wouldn't be out of the lineup.
Some people on the PBE have also been experimenting with an AP build. I wouldn't look to deep into that though, as it's reliant on using your E all over the place and sitting on your thumbs when you have no one else to jump to.
Playstyle
Lots of people have played him to dive enemy teams and cause as much pain and havoc as possible, but I think he's designed with his lore in mind. He can fight and deal damage when he wants to, but his strength is in protecting.Having a spammable knockup as well as an ult that gives you armor penetration, you're far better dealing with tanks that dive your backline. Keeping that all important ADC safe makes your special kind of peel very scary for tanks and bruisers. Making them think twice about chasing someone they need to kill makes you a force to be reckoned with.