We should note that the application itself only includes a few games, but it offers you the possibility to add many more. In other words, you'll have to download additional roms separately, but that won't prove to be very difficult.
To introduce new games onto your iPhone or iPad, your best option is to run a program like iExplorer, which helps you add the roms to the appropriate folder without having to mess with your device yourself. The author's webpage also includes a helpful compatibility list.
The emulator controls are pretty precise for a touch screen. You can even configure them yourself, choosing between many options like how many buttons you want, and if you want the screen in landscape or portrait mode.
iMame is one of those indispensable apps for video game lovers, since it lets you spend hours and hours playing classic arcade games again. You know how it goes - insert coin, and press start.