Thanks for your comment!
It's true that you need to be organised to get to the fifth diamond, and piloting the capsule helps you avoid the dangerous rock piles (which you can spot with the sonar). But you also have to be careful not to let the crystals slip away too much, because after a while it really does get chaotic down there :D! All in all, I think I'm pretty happy with the game's difficulty.
And actually, I don't know at what point I imagined I'd be able to do this game in three hours :/ But once I'd passed the time limit, I preferred to make the game look entirely like what I had in mind (and the sound atmosphere was clearly something I was aiming for with this game).
Thanks for playing!