Hey Paiva,
I tried this game, but not quite sure what you need to do. I came here to see that you said time ran out. I think what's nice is the atmosphere, underwater feeling, but I am not sure what this is in relation to the theme? It's not explained, or at least I didn't get it. I liked the music though!
You also lose the collected thing if you hit the shark? Probably it could be conveyed to the player somehow that sharks are dangerous even for a metallic submarine :)
Some ideas:
- Rotate the player vessel to the direction where it's heading.
- Highlight the collected things somehow so player will notice them better.
- Convey somehow what you need to avoid
Keep up the good work! Cheers!