Personality, backstory and depth make a character for me. Appearance is little needed. But making a very smart person ugly and unhealthy is kind of killing his character if not for an illness. To say a smart person who knows how badly things affect him yet he still uses those things is a sign of stupidity.
Power is as well little needed. For example as Dejavu typed. Kaguya, powerful but bland.
Madara had a very nice attitude and personality, with power to back him up make it very nice.
For a good weak character, he'll have to use his specialty. Lee for example can't use ninjutsu or genjutsu, but a specialist and an expert in taijutsu to back him up. A person who lacks strength goes for speed, Sasuke for example that is. And a person who's physically ill and can't do nothing but a genius can be the mastermind on a strategy and a plan, Kakashi when he lost his sharingan and couldn't try anything against Kaguya for example.
Even the weakest should have their strong points. Their personality is a main point, their backstory should reflect the reason to their behavior, and with that. I can see if I should show sympathy to that character, or see if he had valid points for his actions in his life.