When you live near the core, like I used to, it's impossible to avoid Prince's Island Park. Add to that, the park was my on my walk to work, which meant that for over 3 years I walked through this park daily.
The park is home to several festivals during the summer months. A great variety of events take place in and around the park throughout the year. I have probably attended dozens of them, each one improved by the beauty of the park. With lots of space to walk around, the crowds never seem too much no matter what festival you are attending.
As far as just walking or rollerblading or biking, the park is amazing. I have walked and rollerbladed through the park countless times. There are amazing views, tonnes of sunlight, and lots of other people. If you enjoy watching people (but not through a bedroom window), Prince's Island Park is the place to be.