Improving Anodyne: an idea
[TL; DR: Adding passive abilites to Young through collected cards would make card-hunting a joy instead of a chore.]
I have played this game for 8 hours and must say it is alternately impressive and maddening. Impressive in the scope of ideas explored in a deceptively simplistic representation, maddening in the jump puzzles and the number of times I brute-forced (trying and dying until success) my way through areas (The circus level in particular!).
The frustration of seeing a chest, overcoming the obstacles and enemies to reach it, and discovering nothing more than a card or key inside it rose higher and higher every time until I finally had to put the game aside.
The reason for this frustration is that, as one other poster put it, they are "vestigial" - they have no meaning outside of existing in the game as an N-part key. In fact, you could have made every card a key and the gameplay would have been the same, with the exception that each card is unique, which I will get back to in a minute.
One successful game design concept is to design your various systems so they feed into each other. For example, in System Shock 2, there is a "Research" option that requires a piece of an enemy and a number of periodic elements. When you have these items, completing research provides more information about that particular enemy and gives you an attack advantage over them or reduces their effect on your character. On each floor of the Von Braun, the spaceship you are in for most of the game, you get an email with the inventory of the chemical storage. Each enemy encounter has risk, but is also an opportunity to get a research item to make them easier to defeat in the future. In this way, the research system is connected to the exploration, inventory management, and combat mechanics of the game and becomes an integral part of the game experience.
In the same way, the uniqueness of the cards is where Anodyne wasted an opportunity. Had each card provided some small but significant change to gameplay, I would have been happy, no, obsessed, with collecting all of them. Here are some ideas for how cards might have been used to change gameplay: Collecting the hound card reduces the number of hits to defeat one by 1. Collecting the flame or trap cards reduces their damage or gives you temporary invulnerability (1 hit per screen) from them. Collecting character cards introduces another conversation path with them (which perhaps unlocks another quest). Another card could show the treasure chests in an area. These are just some examples.
Anodyne is a well-done game, with a high frustration factor in parts. By incorporating the cards into the exploration and combat systems, the frustration from nearly useless rewards could be sublimated into a compelling quest for character improvement and a powerful impulse for game completion.