I've always loved Wonderland, more so when i was much younger (and back when Wonderland was owned by Paramount). Definitely a great place to visit if you're coming to Toronto, but if you're only in for a day i'd recommend getting the fast pass (extra $60) to ride without long lines.
The new (to me) rides Leviathan and Behemoth were both impressive, it's been awhile since i've been scared like that! Leviathan was more fun, whereas Behemoth seemed like it was just going up and up and up... then down (rinse & repeat for 3 minutes).
Only reason they don't get 5 stars is because every minute you're there you feel like everything is setup to get the maximum amount of money out of you. From the second you walk in with people bugging you to take your picture, to when you get thirsty and it costs you $4 for a bottle of water.