Try to remind yourself of a melody with some game or movie. Cz was a motivation of Mario, Star Wars, Mortal Kombat, or maybe a pink Panther? And now remind yourself of a game where music has created and supported the building of climate? You probably recall the game, but you can't recall the melody. Why is this?
Melodies that fall into the ear usually have a very simple melody with the main theme. In old games, the creators were limited to just such simple notes, which resulted directly from technical limitations. Hence, there are so many old songs from games that have fallen many of you in the ear: Mario, Pac-Man, Tetris, Pokemon and others. Perhaps if you hear any of these melodies today, you will be able to play the game before your eyes.
On the other hand, we have games in which music does not collapse so much in memory, but is a remarkable role in the creation of the climate. Brad, Ori, God of War, Silent Hill. If you hear any of these songs outside of the game, there is a good chance that you will not associate them with games, and you may not even like them. In games these melodies perform a different function, they do not have to play in themselves, but are to be complementary to the game. Make what happens on the screen reaches you with double force. In Orim and Baridzie The music is gentle, but at the same disconcerting, in GoW enhances the sense of strength, and in Silent Hill overwhelms and intensifies fear.
Some time ago, I watched a boom on hiring whole orchestras to create music. Do you need it? In my opinion there. Often, better results can be used to use two or three instruments. However, everything depends on the game and the effect you want to achieve.
Finally, an example of a combination of a simple melody that well supports what is happening on the screen.