I've tried a bunch of sushi around the GTA, and this place is probably in my top 3. The other reviews make it seem hit or miss, so what follows is my experience whenever going to Yangs for dinner or lunch AYCE.
Service is usually very good. I'm not of Asian descent, and I feel like in some other restaurants this seems to be a problem. In Yangs, they've always treated me exceptionally well. Seated promptly, and constant service. They are quick to remove finished places from the table, and quick to bring out new orders. Always with a smile :)
Food itself is very good. I've tried the menu extensively now, maki rolls, hand rolls, appetizers, teriyaki, noodles, and all sorts of other stuff. The dinner menu has an extra section with about 10 or so more items (more crab/seafood offerings if I remember correctly), but nothing above and beyond. The rolls come with good consistency and excellent flavour for AYCE. I have never left here disappointed or dissatisfied, and I always recommend this place when people want sushi in Markham. Sure, it's not the authentic Japanese sushi as others have said, but again, the food tastes GREAT every single time! I love the spicy salmon, spicy crispy, crab rolls, and shrimp tempura. Never had a bad dish here, and we never leave left-overs!
Cost for dinner is about what you would expect (about $25), and lunch is a bit cheaper in the teens.