I have an iOS game, a fundamentally simple game similar to hangman (except with sheep and a Roman theme). I definitely want to add sound, effects for when a user clicks on a letter or completes a game. However, I have noticed that many games include background music. The ones that don't that I've seen (Flappy Bird, a puzzle game, a word game) tend to be simpler and less involved. Hence my question: is it acceptable for an iOS puzzle/word game to have no background music?
Acceptable? Yes, you can have no music, or maybe some generic noisy background if you want to add something to the full audiovisual experience.
Now, unless you're really short on budget, I'd recommend you to use music for your app. The more original and in tune with your game, the better. Not only because you're creating a full sensorial experience, but because you're leaving out a lot. For example:
There's no deny that music sets the tone for a game, creating moods and enhancing the experience. You'll see a lot of games that have a very snappy and catchy music when you're in the BUYING process, some games have an aural sense of urgence, some games have very low tones that "spike" when the developer wants to catch your attention and so on
Music is at least as brandable as a logo, usually way more. When someone plays a game with a catchy music, that tune will resound in the user's head, something a logo will never do. So people will recognize and REMEMBER your game by that music. And this is why music development for games is the most expensive part of the game's branding: use a good music and it will be a selling point for your game. Use the wrong music (for example, something boring, or that can't be repeated again and again) and your game will probably fail.
Many games get so much recognition from their music that it might be used in additional revenue sources, like CDs, movies, DVDs and so on, adding to the branding I mentioned above AND to the revenue side
Finally, if you decide to use music (which you should!), remember to have controls for mute and volume for those that like to play with no distractions (specially if you use non professional music)
I have my phone on silent 90% of the time and a lot of people I know are the same way so background music isn't much of an issue for me. But I think its still better to give that as an option because plenty of people do listen to in game music, you should make sure of at least these things,
The length of the soundtrack.
How long do you expect an average user to spend on the app per use? If it's going to be more than 5 minutes at a time a track that loops every 60-90 seconds will get old fast. I would try to aim for something about 5 minutes long and/or multiple tracks to cycle through just to mix it up.
Volume and Irritation factor
When some kid is playing the game in the back of a minivan is the parent going to hear it in the front seat? If so how likely will then be to run the iDevice over by the end of an hour long car ride? Or if someone is waiting in an airport is everyone going hear him playing the game?
Can I only listen your your background music while using your app? Can it be turned off? Can I listen to my music library instead? Can I turn off the background music but not the other in app sound effects?