Lost Sea has the looks and mechanics of a game for kids, and elements that would interest a completionist, but it tries very hard to distance itself from those two segments, for some reason.
The game is divided into several worlds, and in each world there are several islands - or levels, located one after the other.
All you really have to do is search for tablets hidden in each island, and the number on those tablets tells you which island in the string you can land on next, until you reach the boss and hopefully beat him.
Levels aren't very different from one another, and seem to only differ in how big they are and how many enemies they house.
Not being able to decide which islands you're going to land on means you can either have a quick and easy time reaching the boss, or you might jump from an easy level to a hard level, to a medium level, and struggle all the way.
If you want any control on which island you're going to land on, you need to find as many tablets in each island as possible, so you'll have a choice of how many steps to take.
You can't combine tablets, and they can't be carried over to the next island. You can only decide between landing on a relatively easy island, or advancing as many steps towards the boss as possible.
Frankly, combat is so cumbersome, regular enemies can be harder to beat than the boss, especially when they swarm you.
To make the game easier you can add companions with various skills to your party, and you can unlock skills using coins you collect in the level.
Most skills are fairly useless, and the ones that aren't cost so much, you'll have to scour every inch of every island you land on to have enough coins to unlock them.
Die once, and you lose all your progress - all skills, coins and companions.
Some companions can revive you, but only once, and you can only save having beat a boss. But it only saves which world you've reached, so dying still reverts you back to the start of that world, without skills, companions, etc.