So with the server issues going down on the North American server, I seized the opportunity to check out Vel'Koz on the peebs. Based on what I've seen both through experiences of my own and through watching others, here's some takes.
Here's my opinion:
Early Game: 9/10
VelKoz's spammable AoE makes him a huge lane bully. His Q can dance around minion waves to strike targets while the rest of his abilities can travel through them with no damage penalty.
Mid Game: 7/10
Crowd Control and burst make Vel'Koz not exactly the ideal mid-game mage but he's pretty good. His high base movement speed (for a mage) allows him to roam and apply his burst and CC both on other lanes and on wayward travellers, or kite pursuers
Late Game: 5/10
Pretty weak compared to what the base damages tell you. The ultimate can hit multiple targets for a lot of damage, but doesn't travel as fast as your cursor does, which means champs with high mobility can mitigate damage; the same goes with his other spells as none are targeted and give most enemies time to react.
Pros
INSANE burst with enough sustained damage to complement
Strong early game
Will not often have mana issues
Kites like a boss
High base movement speed for a ranged champion
Snowballs hard
Cons
No escapes
Short autoattack range (525)
Highly item-reliant
He falls off late-game unless he gets fed
His ultimate requires him to stay in place (although it can be cancelled)
Squishy
Who is he most like?
In my opinion, Ziggs. Kites for days, a considerable amount of CC, some good AoE burst.
What to max first?
No clue, it depends on the situation. I maxed W in the couple of bot games I played; it provides wave clear and a surprising amount of damage, not to mention that's two procs of his passive for another follow up with one of his abilities.
Core build
Liandry's synergizes beautifully with VelKoz's high-CC kit. Rabadon's Deathcap because he doesn't deal enough damage without it. Void Staff to get the most out of your AP.
Standard Build
Pretty standard, nothing we haven't seen before.
My build, a little more defense-oriented
Weird build, but my fave. Vel'Koz is a spammer so Archangel's is a natural fit. This build is more forgiving of slight mistakes while still granting a lot of power. Sorcerer's Shoes for more burst or Ionian Boots of Lucidity, like I have, for more sustained damage and better kiting.