For our game submission (Lumi and the Dark Night), we decided to include some optional goals to allow 100% completion on each level. While not hard-core by any means, it does provide some extra goals for diligent players or those who are just enjoying the game. Each level has some secrets to discover. If you managed to get 100% on all the levels, please let me know. Or even better, post a screen shot of the final level showing your final orb count. (Tip: Use the pause menu to restart Level 2 if needed, and don't take the final lift on Level 5 until you are ready to go!)
Are there other game submissions that included some optional goals with completionists in mind? Golfing Gods is one that comes to mind, but if you included optional achievements in your game please post below.