My review is for tourists as locals have different reasons for visiting markets!
Atwater market is a great place to pick up a variety of goods to bring with you on a picnic near the canal, which is right next to the market itself. The market was easy to get to on public transportation and is also probably an easy bike ride from downtown.
We bought the most amazing produce here- a selection the vendor called "fruit explosion." Everything was perfectly ripe and ready to eat. We also bought some turkey chorizo from a vendor inside (um- yes please!) and two different types of cheese. There is an enormous bakery with a ridiculous bread selection at the end of the market- a carb-lover's dream. We also sat down and had a cup of coffee at a little cafe before starting or foraging for food- very good. There is a newsagents/sundry shop at one of the market as well to pick up bottles of water.
I found a pastry shop that had a selection of macarons and had to have it. I meant to bring them home- something to remind me of my trip to Montreal after I had returned- but I ate them all on the plane the next day. Magnifique!
I'm not sure I'd come here as a tourist if the weather was bad for picnics- unless you wanted to make a picnic in your hotel room. But it was a fun way to spend an afternoon on a beautiful summer day.