I've been going to Sumo on a fairly consistent basis and while it's still my favorite Japanese AYCE restaurant, it's not as good as it used to be.
The food is still very good and I haven't been to any other Japanese AYCE restaurants that are quite as good. I'll mention some below.
Sushi: About as fresh as you can get from AYCE and the rice has a nice flavor. I would prefer about 2/3 of the rice on my nigiri, but AYCE restaurants always try to load up on the rice.
Deep fried items (chicken katsu, cheese wontons, scallops, etc.): Pretty much anything that has been deep fried by Sumo is really good. Always very crispy on the outside without overcooking the insides.
Udon: The fried udon has great flavor and isn't loaded with veggies like some places try to do. I get the chicken and there's a good amount of chicken in it. The udon soup is below average. The soup is a little salty and I prefer when there's a hint of sweetness.
Dessert: While they have standard ice creams, I enjoy their chocolate and strawberry mousse. It's not overly sweet and is perfect to end the meal! I also love their sesame balls. Delicious!
The one thing that has taken a sharp nosedive is the service. The service used to be fantastic with servers who genuinely cared, but this has been replaced by quite the opposite. Last night my server sat me down at a table that was missing plates for a few of us and she didn't set up the tablet. She seemed too busy sitting at another table and chatting with guests/friends. We received more attention when these guests/friends left.
I've also noticed that there has been an increase in the number of items I don't receive after I place my order. This used to be a rare occurrence but now I pretty much expect items will be forgotten about.
Overall, I still think Sumo has the best quality AYCE food in the Markham area. However, the service is causing me to think about looking around for other alternatives.