I've played around with Vel'Koz a little bit and found that his mana costs aren't high enough. He has the ability to just spam his abilities without any real consequences. He can push for days with his W and harass for a long while with his E and Q. The worst part is that this is without any mana regen.
I just feel that he needs a little more of a restriction on his abilities rather than him having almost as much freedom as a manaless champ.
Anyone else feel this way?