If you are from a small town you'll love the Eatons Centre... God knows I did when I first moved to Toronto at 18. Unfortunately the nostalgia has worn off.
Don't get me wrong, the selection in stores at the Eatons Centre is pretty good. Most stores are here and they have the best Apple and The Bay in town.
Apart from those two stores, you are better off shopping along Queen West or Yorkville. Major flagship stores (which usually get exclusive lines) tend to be on one of those two streets and have better selections.