Pros:
Nice baskets. (A short and long basket layout for each hole)
Excellent tee pads (really nice). (Short and long tee pads for each hole)
Very well maintained.
Nice mix of required shots.
Very picturesque.
Nice views. When you are there, it is hard to believe you are actually in Toronto. It feels like you are in cottage country, even though you can still see the Toronto skyline on a few of the holes (and of course during the ferry ride).
Generous gaps, long course with moderate amount of precision required to score well.
I played this course with most of the baskets in the long position, and it is definitely a challenging course. It is long, with a few par 4's scattered throughout. But, it is tight enough that you have to be accurate on every drive. Most of the roughs are unforgiving. If you are careless, and simply shoot for distance on your drive, you'll likely end up in the rough, and it will definitely affect your score.
It is a nice mix of requiring you to be accurate and/or conservative, while definitely testing your long game. It's tough to shoot under par without a big arm. I only had one birdie my whole first round on one of the par 4's. A few of the holes require you to plan your shots. There is a really nice par 4 right dog-leg (when #8 is in the long position) that can lure you into taking some risk...
Nice mix of short and longs, a crew periodically moves the baskets to keep the course seeming fresh to the regulars. I believe they are soon to put in multiple baskets on a few of the longest holes for permanent flexibility in course options.
A few looks for aces, I had a look on #9 that was "oh so close" (basket in the short position).
A nice practice area with two baskets that can really help space out the groups (which is needed, see [*] below).
The ferry ride can be a nice touch if you are from out of town and want to see Toronto. It is one of the nicest ways to see the skyline, take a picture, etc... Plus, there is plenty of other stuff to do on the Islands.
Other Thoughts:
I don't get it. Don't get me wrong, this is a great course. But, between the commitment of time getting there, the ferry, getting into the city, and getting back, the experience on the whole wasn't as spectacular as I'd hoped. Maybe I am spoiled (I live 5 minutes from White Spruce Park in Brampton), but I think a "just as good" or better Disc Golf experience can be had at either WSP or Bronte Provincial Park. Personal opinion: If I were from out of town, was looking for a really great DISC GOLF experience, but had the chance to only play one course, it wouldn't be the Island. The other courses are just that good.
If you do go to the Toronto Island Disc Golf Course, take my advice: go early, take the whole day, bring a bike and a lock, and see and do more there than just Disc Golf. Take a tour and enjoy the rest of the island and the scenery, then it will truly be worth the investment of time.