I only come here once, twice max a year and I'd say I have fun each time.
Considering it's the only amusement park closest to me, I have no other choice but to come here when I'm in the mood. It pretty much has everything from roller coasters (Behemoth & Leviathan!) to water parks to theatres and even a kid's zone. The only other amusement park I can compare it to is Lotte World in South Korea which is a dual indoor/ outdoor park and that was great.
The lines are relatively long during the summer, but that is typical of an amusement park. There is a fast pass option for those with some extra money and little patience though. The park itself is huge and you should expect to do quite some walking throughout the day.
In my opinion, the park has little re-visit value which is why I rarely come here. I only do so because I get free tickets... haha.
Canada's Wonderland is definitely worth a visit though if it's your first time and if you're in the area of Vaughan or willing to travel.