I do agree game music has declined and most of it tries to resemble ‘movie music’. So why is this? I don’t know. How about a theory?
Great game music seemed to be written by gamers with musical skill. Today, it seems game music is being written by musicians who may or may not be gamers. I wouldn’t be surprised if these game music makers are just using video games as a stepping stone to get into Hollywood (where they would rather be).
I also think game designers got old and became fuddy duddy. These gray haired developers are out of the time. They are old men and listen to old men music. But when the flower of youth is freshest was when they really got in touch with their ROCK AND ROLL. Video game music was like an explosion of youth… mostly because video games were made by young people. There were no old fuddy duddies in gaming at that time.
When gaming first went to CDs, we got an idea of some of this ‘explosion of youth’ without the chip tunes. But once music could be done with CDs, they brought in musicians who said, “We must be like Hollywood music. Only music there can be!” Bah.
Above:  Even the company logo orgasms as the chaos is shown after Einstein kills Hitler and returns to the present. You never see something like ‘Westood proudly presents…’. It is always just the company logo now, just the brand. Apparently, no one is proud to present anything anymore.
Above:  Star Control 2′s music was mods that were done totally from contributions from young people on the Internet. Songs like this would never be in any movie. It is very energetic in a youthful way. It is also trance-line. We like our video game music to put us in trances.
Above: Another song which would never appear in a movie. Yet, it works in a game.
Above: Emailer mentions F-Zero so here it is. Amazing tune.
I need to investigate this myself, but if you go back to how music was done centuries ago for various plays and chorus themes, I bet it sounds like video game music. Could video game music be the chorus of the gods singing your way?
Above: With games like this, it is no wonder the NES was revered.