This is a very very very bias review! I try to fly through Pearson as little as possible only because of the staff.
The airport itself is very large but it's outside of the downtown core and takes some time to get to. Pearson has some solid amenities with a large selection of food places (though overpriced), a big duty free shop, clearly marked signs, tvs around the gates and now free wifi! That would normally make it a 4 star for me.
However the following really irks me about Pearson...I always feel like sheep in a mosh pit at a heavy metal concert being herded by shepherds who hate their job and feel like they have somewhere better to be! I know that's not true for all their employees but a bunch that I've dealt with have always made people in and around me feel that way.