I've found a decent workaround using the "Brightness" app from the AppStore. After installing the app, go to the app's settings (click the "i" in the circle at the top of the screen) and toggle ON the "Brightness Control" option. This will put the app in the Notification Center, where you can access it by swiping down from the top of the screen. Once you've got it in the Notification Center, you can also adjust the position of the app among the notifications to be near the top, so it's easy to see and get to without having to scroll down among your notifications. After following these steps, adjusting brightness takes these steps:
1. Swipe from the top to reveal the Notification Center
2. Tap the Brightness notification (the message with the blue dot next to it)
3. Slide the app's brightness control slider to the desired level, or tap one of the presets you've created.
This is about as close as I can get it to the iPad OS experience, where you:
1. Double-click the home button
2. Swipe to the right to reveal the brightness slider at the far left of the apps and settings
3. Slide the brightness control slider to the desired level
Why Apple doesn't make this functionality/user experience identical across all mobile devices on their OS is beyond me. I use this feature every day, many times a day.
Without it, the steps are:
1. Home
2. Settings
3. Scroll down
4. Brightness
5. Slide the brightness control slider to the desired level
Of course, if you keep the Brightness setting open in Settings (rather than exiting out of it inside of Settings), you can reduce the steps to:
1. Home
2. Settings (lands you in the Brightness panel)
3. Slide the brightness control slider to the desired level