http://i.ytimg.com/vi/7o6U-fPdhCQ/maxresdefault.jpg

I agree that Veigar's E was problematic as, essentially, a very strange "skillshot" that he had to land on the edge. (Full disclosure: I always sucked at that, so I may be biased.) The problem is that they've removed the edge-stun mechanic but haven't replaced it with anything. What we're left with is a zoning barrier that only stuns a target if they choose to run into it.

Here are some ideas. I'm sure people can think of better ones. But let's at least get a list going for Meddler and the other Reds, to encourage them to not "Cass" Veigar by carving away his unique abilities and then giving him pure numbers buffs until he's viable but boring.

Create a real tradeoff

Give Veigar's opponents a reason why they might want to stun themselves on the edge instead of staying inside the cage.

Right now, Veigar's stun works only as a zoning barrier. There's no reason why anyone should ever actually get stunned by it. If we want to keep a stun as a big part of Veigar's kit, and we don't want Veigar to be able to insta-stun someone by placing the skill just-so, we pretty much have to come up with some reason for the enemy to potentially want to stun themselves.

There's already a very limited exception: if you're fleeing from or chasing Veigar, and he hasn't leveled his E up very much, you might want to eat a 2s stun rather than waiting 3s for the walls to go down. But other than that, the only way people get stunned by it is if they don't know how it works or panic.

Perhaps there could be some way to create such a tradeoff. For example, maybe it shreds MR while you're inside the cage, but you lose the debuff if you run into the wall. Basically, that would create a tradeoff between dodging spells (Q/W) that will hit extra-hard if they do land and taking a guaranteed full rotation at less damage. Or you could increase the amount of time before the walls collapse to 5s, to match Anivia's wall; that'd make it a more serious tradeoff between being zoned for 5s or escaping the zone but getting slammed with a meteor.

Or you could give Veigar's meteor (Dark Matter, W) a reduced cooldown if cast in the central part of the cage. This would make it less costly for him to sling meteors at you while you dance around inside the cage. Someone might choose to eat one meteor and get out of the cage than to risk being hit with two.

Stun caged targets if struck by Q

Give Veigar a way to stun targets by landing a "real" skillshot.

Another option for retaining a stun mechanic: if a target is struck by Q while inside the cage, they're immediately stunned. Veigar's stun would become a 1-2 punch with more counterplay: he throws the cage, but only gets to stun you if he tags you with a skillshot.

Mana drain (or cooldown amplification)

Make it costlier for opponents to fight Veigar from inside the cage.

Manaburn is a classically "anti-fun" mechanic, but maybe this would be one place for it: while inside the rage-cage, targets' mana costs are increased by X%. Alternatively, it could just increase cooldowns of abilities used inside the Event Horizon, alluding to the time distortion observed near a black hole.

Simulate a gravitational pull

Slow targets more the closer they are to the center.

Of course, Veigar doesn't necessarily NEED a stun, so long as you replace it with something.

A "gravitational pull" effect, slowing targets more the closer they are to the center, would certainly be themely. Also, in addition to representing the black hole phenomenon the spell is named after, this would create a somewhat interesting choice: running toward the edge makes it easier for Veigar to hit you with a meteor, while staying in the center keeps you further from him and slows you more.

Cooldown reset

Reward Veigar for getting kills on a caged target.

Another idea: if Veigar kills an enemy while they're inside the Event Horizon, the cage vanishes and the cooldown on Event Horizon (not his other spells) is reset, allowing him to throw it again. This would reward Veigar for managing to kill a target inside his cage by allowing him to throw it again to help his team.