In my opinion, games have been around long enough to have discovered some principles that just work for gamers, yet I continue to see games come out without some or all of these options. Below, I list the items I consider "necessities" that every game should have to make them user-friendly, in order of priority.
*Invert Y-Axis
We older gamers grew up in the era of space flight sims, and we're used to aviation controls. Most games, to their credit, include this option. However, there are a few exceptions. I will often stop playing a game if I can't invert the Y-axis, since my old habits die hard.
*Minimum of 3 Difficulties: Easy, Normal, Hard
Not all of us are hard-core frag fiends. Zone of the Enders and F.E.A.R. got it right in describing their "easy" mode as a mode for "new or casual" gamers. Some people play on easy because they care more about the story than the gameplay. But for those of us who are hard-core, the normal difficulty may be too easy. Including at least three difficulties catches the majority of gamers.
*Subtitles on/off
You may be incredibly proud of your voice actors, but that doesn't mean everyone can appreciate them. What about people with Mono TVs? I happen to live near a very active railroad track, and it's not unusal for trains to pick that critical plot moment to rumble by.
*Mid-mission checkpoints
You don't have to be Halo, with checkpoints every other step, but mid-mission checkpoints for missions longer than 10 minutes are very important. Not all of us have the freedom to sit for hours on end playing the game, and there are few things more irritating than having to play through 20 minutes of easy gameplay over and over because of that one enemy you can't defeat. Lack of this feature almost singlehandedly broke Ninety-Nine Nights.
*Pause cut scenes
As an older gamer, I have lots of demands on my time. It's incredibly irritating to have to choose between watching a cutscene or treating my child's ouchie. Xenosaga Episode One's 30-plus minute cutscenes were notorious for interfering with my family life. I was very thankful they added the pause option in subesequent chapters.
*"Continue" from opening and "Game Over" screens
Let's face it - nine times out of 10 gamers want to pick up the game where they last left it, regardless of how many profiles or saved games they have. A "Continue" option that automatically loads the most recent saved game seems like a small way to benefit your customers. One of the most irritating games I ever played required me to go all the way out to the opening screen to load a game upon death. That game is no longer in my collection.
*Brightness/Contrast/Gamma adjustment
This is particularly necessary for games with dark environments. I have played a handful of games in which I was unable to pass a certain point until I turned up the contrast on my TV/Monitor because I simply couldn't see the environment I was supposed to interact with.
*Effects/Music/Voices sound options
Similar to lack of subtitles, it's irritating when a game's wonderful sound effects drown out the voices that are advancing the plot or issuing your next mission. Many a shooter have I had to pause and check my objectives because my orders were issued during a fire fight, and I couldn't hear them over the gunfire.