I went to Harbourfront Centre not too long ago with some Yelpers for a film screening, and was pretty pleased with the results.
Sure, there's the issue of noise from planes and the pretty heavy crowd, but I really had no issue with it at all, and was able to enjoy the film. I suppose my only complaint would be the somewhat uncomfortable seating, but what can you do?
I had never watched a film outdoors before, and watching one lakeside on a warm summer night was great. I would definitely do that again.