There are many factors, including…

• Ease of reading (composition)
• The theme you wish to convey  (a dramatic panel or scene)
• Attractive art style
• Rhythm of dialogue
• The ability to “direct” the flow of story, and introduce developments that wow the readers.

Creating a manga is like creating a movie or stage drama. A manga creator is like a mini-director who undertakes everything from the plot, direction, setting, make-up, design etc all by themselves. Personally, I like to put the above 5 points in a graph (see below) when evaluating manga. What is the basis of my evaluation? Whether it resonates with my heart or not!

First of all, I must be able to comprehend the creator’s strengths. Next, I must ensure they resonate with as many other people as possible, then we can go forward with developing the manga. 

This is how I determine a successful manga idea.