I really feel like I am deep underwater, good atmosphere. The gameplay is simple and common. But with the setting and light mechanics it adds up to creative input that works. It does felt repetitive and stale the longer you play but I understand that simplicity is a priority for short time game making.
If you want to expand this, maybe add some upgrades: light range and wideness, damage, and some abilities. Abilities like throwing a chain hook that when hit a rock/platform you will be pulled there, a 360 degrees swing attack, etc. I just suggest these to add variation to player actions.