One of my very favourite spots.
The ferry is so inexpensive- I think 6.50? and there is a ton to do! A lot of other YELP reviewers are correct on here that the ferry to Center Island, and Center Island itself, are kid-filled and loud, and I agree, but I think it's nice. I took a fair few trips here last summer! At one point my cousin and I (I am in my early 20s, she is in her late teens) went on a few of the "kid rides," including the Ferris Wheel and the (Skyride?) where we got to look over the whole park. I found it very enjoyable.
The outdoor restaurant on the Center Island part wasn't bad, but I feel I like Hanlan's point the best. I didn't visit the nude beach, but I would swear that I got the best spot in the house in a little sandy pit on the edge of Hanlan'd Point to watch the Canada Day fireworks! It was amazing. Going to Toronto Island is a welome change for me (as much as I love the city, I really like the green! It's a very relaxing place.)
A few more points:
Pluses/tips:
+you can rent a bike for hours, or the whole day
+the bikes come from single, all the way up to.. I think 6 people? Very cool.
+There are tons of beach spots
+BBQ pits!
+Lots of places to sit, even when busy
+Check out Hanlan's point for an incredible view of Toronto
+Water taxis can take you back to the city if you miss your ferry, but ferries are frequent
Minuses/
-Bring a picnic for a day trip. The restaurants that I have tried were expensive! If you eat on the Island, I suggest a full Pizza at Pizza Pizza split amongst you... but there are plenty of places to picnic and that makes it more fun!
- Mosquitos are frequent at night!
-Last ferry leaves at 11:30 ish so you want to be sure to get there by then
Bring a book, sunglasses & sunscreen :) Perfect summer place!