Thanks for the great feedback!
It was a big concern during development.
Basically, we made the bet that most players would not get the "optimal" way of playing right away with the little information they have (no gauges, HUD, possibly no prior walkman knowledge...) and the short nature of the game.
Now, the interesting thing is that players either found the game too easy, balanced or too hard!
With some more playtesting, we can probably find the simple trick that makes the experience better for everyone :)
(I think dynamic diffulty would be very fun to implement here)