1. Her snare not only lasts for an insanely large amount of time compared to other stuns in the game, (even with the Tenacity bonus) but it deals damage, too. This gives her poke and the ability to completely stop other champions while she can take all the farm, and easily burst down an enemy champ in a very little amount of time. Maybe take away some damage or at least reduce the time a champion is ensnared.
2. Her pool stacks damage? Combining this with the snare is too much. Nerf it to damage per second or just nerf the AP ratio.
3. Her passive pretty much gives her the ability to stay in lane almost as much as she like, continuing to use her abilities to not only heal, but completely destroy the opponent's laning phase.
4. Her cooldowns should be slightly longer, she's able to use the snare and pool combo a little too often.
5. She's doing a lot of work in team fights. She can easily single one person out of the enemy team and everyone targets them. By the time said person has been targeted, whether they were killed or not, that combo is already up again to single someone out.
6. I personally think her ultimate is fine.
1. You've recently balanced his Q to give him 2 AP for killing champions, larger minions, and larger monsters. I think this is good.
2. His burst is a little too much. Granted he hits the stun (which is way too easy to do) he can then use Dark Matter to completely wreck the enemy team down to half health or lower. In addition to this, his ultimate has an insane AP ratio to it, plus 80% of an opponents ability power? Too much. Veigar can completely dominate any AP champ and destroy their laning phase so long as said player knows what they're doing.
3. Just like Morgana, Veigar can easily single people out of the group and mark them for death. Maybe make his stun duration a little bit less.
4. His stun's cooldown is pretty short, too. If he misses it he can just wait a few short seconds and try the combo again.
I could post more, but these are the ones I'm the most unhappy with.