I think that to make a winning game, apart from marketing that is definitely the decisive phase, it takes an interesting history and not just a simple idea; obviously there are exceptions fore some important ideas, such as the successfully ideas of Tetris, Bubble-Bobble, Arkanoid, and so on.
There must be an interesting protagonist, both as a representation and for its abilities, there must be relationships not only with objects / devices, but above all with other creatures / characters (eg enemies).
Design is the main thing, but the work to be done is very large, requiring more people: designers, charters, programmers, music experts, beta-testers, marketers ...
How can you think of getting this all by yourself?
Then, try and "trying is not harmful"; whether it is just to have personal satisfaction and not a gain, sooner or later we find the right way, which is consistent with one's own abilities and style.