This is easily my favourite bookstore in the city. The entire third floor is devoted to comics and on its own would be a fairly good comic store. The basement houses some used music CDs and the main 2 floors are all books. You can't really come here looking for something specific or brand new, so if you want that go to an Indigo/Chapters or better yet just order it online. Instead, you just come here to browse and explore, and you can almost always find something interesting in awesome shape and cheap.
Be prepared to part with some of your money if you visit: it has that effect.