Oyster Boy has - you guessed it - great oysters. Also, great fries, and really hospitable, friendly service.
I like oysters a lot, so I don't personally have a lot to say about the non- oyster dishes (I'm pretty easy to please at this place - I go in, order a bunch of oysters and some wine, and leave very, very happy), but I've gone there with people who don't like or are indifferent to oysters, and they've been really happy with their meals. The fish and chips are particularly good.
This is one of my favourite places in Toronto. I ordered oysters here for my wedding. Reservations aren't strictly necessary - they're happy to seat you at the bar if they're full - but are helpful especially on weekends because it's a small restaurant.