I combine many genres into one game,and it looks like a mess

Every time you say something, the goal is not to expound the entire truth of the universe. Sometimes you say things to motivate a person, or to help them focus, or to poke a person so they'll do what you want them to, or maybe you just want a laugh.

As mentioned, prerequisite to any success is that person does the hard work of getting started and making study and practice a habit. It is essential. The goal then is not to speculate about what makes commercial games monetary successes. That's way out of the ballpark.

 

This is where you are completely incorrect. It's like saying that spaghetti bolognese is no longer competitive, so you will throw the whole fridge and the kitchen sink into the pot to make the recipe 'stronger'. It doesn't work that way. The best things in life and art are always simple and elegant.

Become better at it then. Play the games you like. Study them carefully. Write a 50-page report on how to make a particular type of game, complete with case studies and examples. Create demos that try to be really good at one or two simple things, and polish them until they shine. I guarantee that in no time you will become better than 99% of the devs on the planet at making whatever it is you want to make.

 

Combining genres is not bad by default but it is often best done in moderation and in a manner that is not jarring. So for instance you have a game like Ratchett and Clank, it combines platforming and shooting, but it may also have racing segments or other mini-games inside. It's good fun, well executed. But then you have the racing segment in Mafia that was pretty much universally despised, like even the creators of the game themselves said they hated it. Point is, good execution is key, but that's not going to be easy to do when you have too much you need to execute. It would be like a balancing act that is impossible without 7 extra arms.

As you add more, depth will likely decrease. So yeah Ratchett and Clank may have a racing segment, but its mechanics are not going to be as solid and complex as those in a game like F-Zero GX, or Mario Kart, games solely devoted to racing. It just gets the job done in giving the player a more varied gameplay experience that remains fun and refreshing. Also the different genres as they stack up should not require the skills of genre experts. So if my game is 90% platformer, if I include one FPS level for whatever reason, that level should not require counter-strike skills to complete. It should ideally try to be a fun experience manageable to people who are not normally FPS players.