Oysy is a definite plus in the Madison dining scene. It's not much for atmosphere--looks like it might have been a Ponderosa in a previous life--but the food is the emphasis here.
The variety and value compare favorably to the places you find in bigger cities and on the coasts, like Todai. The freshness is maintained respectably (given the lack of mobs of starving Asian diners more typical of a Bay Area suburban buffet) by the kitchen preparing relatively small quantities and refilling the stations more frequently.
The dim sum selections are less appetizing than the sushi. Skip the fried and steamed rice and use the sushi rolls to get your starch. The cold snow crab is always a winner, along with the steamed flat fish and seaweed salad.