Me and my coworker came here for lunch on a Friday and it was packed. Luckily we got seated soon. I've had my fair share of Souvlaki and I would say although Loui's Kouzina's was better than chain Greek restaurants, I've had better. The meat was succulent but in my opinion could've had a bit more flavour. The potatoes that came alongside the souvlaki also lacked flavour.
We also got the 3 dip pita platter, and it was also mediocre. I've definitely had better hummus and tatsiki elsewhere. The staff were friendly but very busy running around.
I would say if you are in Markham, Loui's Kouzina is a good option for Greek food, but I wouldn't make the trek here if I was in another part of the GTA.