Loot the Game. Yeah even though it was made by John and was one of his last games, but it just felt like there was really no point to reach the end. Adding quests though will actually mean something.
Oooh I was gonna shout Sonny series until my pants fell off but Freakenstein beat me to it! Also Stick War 2 sounds good, maybe Amorphus Plus, Colony and other multiplayers/MMOs.
Any new game you guys make should have quests. Then the most popular games you should try to. So Raze, Achievement Unlocked, Sonny, Strike Force Heros, etc. I don't know if you have to ask the creators to make the quests or what.
The Learn to Fly games were a good series with plenty to have quests for. Villainous was a great game, and it's also got enough there to have plenty of quests as well.
this is just a suggestion to make the quests a bit more organised how about a option to show only hard quests or medium quests or easy quests and to show least quests earned most quests earned, and not to show quests finished, show quests finished. You get the idea right?