Manual enables you to tweak every setting before taking a picture, so you get the perfect shot.
Unlocking capabilities: Manual unlocks a wide variety of settings, so you can customize your shots.
Live histogram: The live histogram in the app lets you see how many of the pixels in your image are dark and how many are light. This provides you with great real-time feedback, so you can decide how to adjust your settings to get the best possible image quality.
Learning curve: If you're not an experienced photographer already, you will find a steep learning curve around adjusting the settings for optimal picture conditions.
Touchy controls: The control system in Manual could be better. It's a little finicky, and sometimes it is difficult to get the program set on the exact specifications that you're looking for quickly and efficiently.
If you want more control over your photos, then give Manual a shot.