I actually did the quests on schedule, meaning I did each campaign's quests when I was the proper level for that campaign. The only exception is that it took me longer to do all the AO3 quests so I didn't finish until I was around lvl52 or 53 and also I did the frozen nightmare quests when I was late 50s-early 60s.

So lots of them were very tough and time consuming for me. I can remember the swamps and croc fued ones being tough. But I guess if you just level up fast and then go back to do all the quests, then most will be rather easy.