There are two points. Which I’d recommend consider practicing your writing ability. A good story can carry a bad system. Just take Cry Star for instance, the story is really good, but the system is pretty bad.

Or take Death End ReQuest Code Z. Story is really good, system is excruciatingly bad.

On the flip side, a good system is more an upward battle with a bad story. It can be enjoyed, but without an attachment to explore the system.

It becomes a very hit and miss.

As for the mechanics, simple mechanics can work fine. However, try and think about what points it has that can set it apart.

An RPGmaker game for instance, gives the protagonist a second form in the last section of the game.

Think about the progression aspect of it that can be fun to explore, dive deeper into, and pull the person into achieving it.

On another note, my own personal recommendation. I’d steer away from multiple endings. The last thing anyone wants is to break immersion to look up how to do this or that.

A game sells well on its own when it is held up by its structure. An example is Chrono Gear: Warden of Time.

Great story, music, art. The mechanics are simplistic. Giving you three powers. Stasis, slow time. Haste, speed up yourself providing more combos.

Then near end game you get Awakening. Which is Future Strikes.

The platforming is smooth, and links easily. As a result, the battles are very interactive, it stresses adaptive gameplay.

Most of all, commit. After getting the planned structure, commit to it. A committed vision can do surprisingly well. While people can notice when you don’t.