Squishy AF
No mobility
Has to level up the stun to keep you in place long enough to hit with Dark Matter consistently.
All-in types like LeBlanc, Fizz, Zed, etc all excel at 100-0ing the short stack. As well, champs with very long range poke/harass (Xerath, Ziggs, Nidalee, Lux) can all safely poke Veigar down without being at risk.
Veigar is a huge threat if, and only if, you play passive in lane. If you let him farm to his heart's content and never harass him or try to push him out of lane, then yeah you're gonna have a bad time.
Also, fun fact; if you're caught in the middle of his stun, and not in immediate danger, your best option is to actually turn and engage rather than run into the damn wall like a lemming and leave yourself open to be taken out (Much like how it's better to turn back and get closer to Darius rather than try to outrun him when he's winding up his Q).
Counterplay exists.