The Veigar Changes don't solve anything
The Veigar changes are not going to go well at all for a number of reasons. I'm going to go through the changes now and explain now:
Passive - I am extremely disappointed riot didn't take a look at this passive. Whille a new one could still retain him gaining mana back, this is one of hue he least interactive and boring passives in the game.
Q - Baleful Strike Changed to a skill shot that stops on the second unit hit Grants 1 AP for each unit killed Range increased to 850 from 650 Cooldown changed to 7/6.5/6/5.5/5 from 8/7/6/5/4
This is the first good change on this list. It makes him risk something to use his q while buffing its potential and giving him team fighting capabilities.
R - Primordial Burst AP Ratio reduced to 1.0 from 1.2 (Ratio on enemy's AP unchanged) Mana Cost flattened to 125 at all ranks from 125/175/225 Cooldown reduced to 120/100/80 from 130/110/90
This is where things start to get bad. The mana cost and CDR reduction change are fine, but lowering the ratio is unnecessary especially due to the change below. Mid and early game with that damage nerf he will rely on landing a W Q and R to kill someone, which is impossible due to the change below. Which is the main problem
E - Event Horizon Has a 0.75 second delay with a warning particle before the walls appear Mana Cost decreased to 80/85/90/95/100 from 80/90/100/110/120 Cooldown reduced to 18/17/16/15/14 from 20/19/18/17/16 Range increased to 700 from 650
Riot, after all do the creative ideas you could have done to completely change the ability, you gave it a delay and called it a day. I'm sure this looks fine on paper but think about it. Almost every Veigar caught people out at max range with this ability due to its short range. Now with the delay it's IMPOSSIBLE for him to catch people out, which in and of itself isn't a bad thing. However, his W is 100% reliant on landing his E. The circle is way too large to trap someone in it and somehow land a w. This combined with the ult ratio nerfs will makes I'm not able to do his job.
Another note, Veigar now has no way of defending himself from assassins or tower dives. He will put down his E and any champ with mobility will simply kill him before the walls even come up.
W - Dark Matter Mana Cost reduced to 70/75/80/85/90 from 70/80/90/100/110 Cooldown reduced to 10/9.5/9/8.5/8 from 10 at all ranks
But it's alright we got a lower cooldown on W. 10/10
Conclusion/TLDR: The changes make Veigar never able to land W, the ult damage nerfs are unnecessary, and the E change makes it impossible to catch people out or peel for himself. He will basically be completely useless VS assassins and not to mention tanks that are locking him down. I am severely disappointed with this rework and hope Riot gives him some form of staying alive or just completely change the E ability, which I think they should of done in the first place.
These changes keep his damage the same, but make it IMPOSSIBLE for him to use his W. Which is a big problem. If riot somehow makes him able to land it more consistently without making it broken, I would be so happy.
KEEP IN MIND: I realize this is PBE and things change, I am basing this post around what they said specifically about number changes.

player, I have to live with my main CC having a 1.5 seconds delay on a similar area, and ALL of my kit relies on landing that one.
can be more flexible with his rotation and gameplay. Just because they took out a little bit of damage and gave a really short delay on the stun doesn't mean it's a "nerf", you're just exaggerating.