Picture this: you're reading a fantastic book, completely engrossed in it, eyes glued to the page with no thought of setting the cursed thing down. Your mind paints vivid pictures of its interpretation of the language it sifts through, and perhaps you're even reminded of a tune you carry fondly. The song, while fitting, is likely something you've already heard several times over, but all the same, it combines with your mind's eye and forms a lasting memory. This mixture coalesces into a form that strikes you as awe-inspiring, perhaps even motivating you to read more, maybe even to create your own content! This feeling of emotional liberation lasts with you for some time to come, rousing your muses and igniting the spark that moves you.
Enter films - moving pictures showing one person's view of a story, accompanied by special effects, music, and varying degrees of acting prowess. While the combination of these things may be effective (most people would look at box office figures to determine if a movie was 'successful', though money doesn't always tell the truth...), we, the audience, are often limited to one or two particular views of the work as a whole. Music accompanies film and has since even before our moving pictures' audio made its way into the mix. Film scores do their very best to reflect the vision of those producing the films themselves, but are often limited because of that style of execution.
Finally, interactive games enter the fray, some as simple as PONG, others almost literally interactive movies like any triple-A title these days. The visuals change entirely on what the player decides to execute - even if the decisions are "wrong" or result in "failure". The audio, however, follows the player character's actions quite closely: a paddle moves to hit a bll and a blip is emitted, giving an audible cue for "HEY!! You did something!" While simple diddies, bleeps, and boops, these audio cues were the first music in video games, forming the ever-popular group of tones we call sound effects. As technology advanced, we were gifted with monophonic (that's 'one-note-at-a-time melodies for you non-music folks) accompaniments to our video jaunts. Stepping forward even further, we encountered polyphony - many sounds at once - leaving the next advances to give us varying electronic and percussive sounds, culminating finally in live orchestral (or even rendered!) pieces in the games we play today.
"Okay, so the march of technology is ever-progressing, fine, I get it!" Even still, game music differs from its competition on a level the others can't even touch - it reacts to whatever inputs the player character gives the game. Granted, this might be a simple sound effect, but think about the last time you completed an objective in a game: you heard some kind of fanfare, right? The Legend of Zelda is a cult favorite for its many victory diddles, along with damn near every other RPG, adventure game, or the like. Encountering a locked door in Chrono Trigger results in a mysterious melody that leaves the player wondering if they've yet to discover some huge truth. Critical HP in Pokémon actually makes players nervous by emulating a heartbeat, and in generation five and later, even discordant music to accompany! Moving in complexity, different areas of games often have their own music, and heck, even particular events in the same area might be accompanied by a change in mode, key, tempo, or even an entirely different track.
The point here is that because video games are essentially interactive fiction, audio becomes much more important. Rather than simply sitting in the background and being important on various cues or hits, game audio can change and mold itself around what the player decides to do. Effective manipulation of audio in games makes for a FAR more immersive experience - one that simply isn't possible in other media. Writing engaging music and incorporating effective psychological effects with your content can leave the audience spellbound in all the best ways. Keep an ear out for previews and ideas down the road!
