Less is more

I often say this - when it comes to audio, often times less is more. And by that I mean that the less someone notices audio, wether it’s in a game, movie, commercial etc, the more they will be pulled in to the experience. In other words, the best audio is usually that which you do NOT notice. Think about it - you go to an event of some kind, if you have young children perhaps a graduation ceremony, or some sort of public performance like a play or an awards ceremony. There are many sound related events happening - there are usually several live microphones for people who are speaking, music cues that start and end, maybe some slide shows or videos that have sound. Everything is moving in real time, and there is sound for each thing. But you, sitting in the audience, will take no notice of the sound - UNLESS SOMETHING GOES WRONG. The microphone cuts out or starts to feed back, the slideshow starts and there's no sound or it comes in late, the music cues play and they are too loud or not loud enough etc. THEN you will suddenly notice it as will everyone else. If the sound person has done their job correctly, you won't notice a thing, despite the fact that he or she is juggling many different things. 
It's the same for anything with sound. Video game sound, when done correctly, will simply pull you further in to the immersion, but you won't necessarily take notice of it. If something is too repetitive, too loud or soft, the dialog lines are uneven in tone or volume, the UI audio is too much or too clunky....whatever. 
I've played a number of mobile apps recently, and as an audio professional, it's pretty easy for me to tell when the audio was done by an engineer or someone else who "knows how to do" audio but isn't a dedicated pro. They are outside of their discipline, and they are not familiar with the complicated processes that it takes to make even simple apps sound in such a way that it becomes seamless to the player, and un-noticed. 
Audio should always compliment, and not over-take the experience. In this way it pulls the listener further into the experience. An nothing will pull them out faster than bad or poorly integrated sound.