You need to keep people interested in playing the game and interested come back to play your game again, isn't it? You don't create game just for you...
Keep your priorities straight. It should be:
1) Make something you want to make.
2) Make something you will have fun making.
3) Make something you will learn from.
1058) Make something that other people will like playing.
Trust me. You really should not worry about making your game marketable (because that's what you're worrying about right now). If you make a game that you love then it will be fun and therefore it will be marketable. But if you make a game because "that would be something people would love to play" or "that would be something that would make me a lot of money" then you're totally in the wrong ballpark.
Facebook was made because someone wanted a tool for easy communication.
Google was made because someone wanted a better search engine.
Dell was made because someone wanted to construct cheap and affordable computers.