Manual has great tools, but the controls are lacking (pictures)
The Manual controls are a bit wonky, but the basics are there. Pro photographers are going to love the new freedom iOS 8 provides.

Manual for iOS
Manual controls
The first time you launch Manual, you're guided through how to adjust ISO, shutter speed and exposure.
Along the top is where you can find the extra settings for white balance, manual focus and flash.
Automatic mode
When both ISO and Shutter Speed are set to auto, you can still control the overall exposure of a photo. This slider reproduces the same functionality found by moving the sun icon in the stock iOS 8 Camera app.
Picking with a picker
The picker, shown here, is for shutter speed. As you can see, it leaves little room to move your finger to the right, making it difficult to scroll around with ease.
The ISO picker, to the left of the shutter button, functions in the same manner.
Settings
The Settings portion of the app offers few adjustments. You can set your preferred grid, select a theme or disable sounds.
Example
The photo on the left was taken with the stock iOS 8 camera app, with the focal point on the middle of the tree.
To the right is a photo I took with Manual, adjusting ISO and shutter speed.
As you can see, the photo taken with Manual is better exposed, with more accurate colors.