I've been reading the reviews, and the complaints you see are very much the same issues that could arise with ANY airline, anywhere.
No leg room, bad service, overbooked, late, delay etc etc are issues that anyone who travels a lot has encountered and they are not just unique to Air Canada.
Admittedly, I am a bit biased. I am a Super Elite 1,000,000 mile member with Air Canada. Yes I get perks because of that, but there were many years of non status flying with them I had to do before I got to this status. Even so, I still encounter some of the aforementioned issues. I just returned from St. Lucia on a Rouge flight. Rouge tends to have less legroom than others and the seats are not very comfortable, but I knew that going in. The staff was wonderful though. I recently had delay after delay when trying to get out of Toronto to Heathrow etc. The more you travel, the less affected you become by the issues that drive infrequent travelers nuts. Don't get me wrong....I get that it is very frustrating. But when you are a very frequent traveler, you learn that stuff happens, no matter where you are and you have to go with the flow. Easier said than done, I know. But if you are expecting to jump on a plane and have all the comforts of home and have everything go 100% smooth all the time and no issues, then you're better off taking a train.
I've traveled on many different airlines over the years, and I really can't think of one that I would not fly on again. I'm always very happy to see an Air Canada plane when I've been over seas for an extended trip. I've always been treated well, have (knock on wood) only had my luggage lost ONCE in over 25 years of frequent flying with Air Canada, and have the utmost respect for all on flight staff.
I'm proud to be an AIr Canada customer and hope to continue doing so for many years to come.