When playing veigar it always feels like much more than .5s. Sometimes I wonder if the .5 has gone by, but the game isn't checking enough to see if somebody is occupying the space for the stun often enough so occasionally it may not register someone as stunned even though they should be(similar to how a raka e may not always silence targets coming out of statis and such.)
In other news, I believe that veigar could at the very least use some touch ups on visuals. It can be difficult sometimes to measure where his w is at in terms of a safe and not so safe zone. His E can sometimes be a bit misleading as far as how close to the wall people have to be before it will stun.
As far as balance changes, his E is fine. If you have flash up, chances are that being caught inside his e is a death sentence(granted veigar has teamates nearby to assist in the damage) as people cant dash through it without getting stunned. Veigars E, unlike many other abilities such as a blitz hook, can actually stop a tristana in the middle of her jump.