But if greatness is just a neutral measurement, is it actual desirable to achieve it? What about a "great leader" who leads his people into war after war?

I think "greatness" is anything that can be defined as "great". Surely one can be 'great' or do great things in either a positive or negative context.

I think greatness can be found in even the smallest of actions - anything that makes something "considerably above the normal or average".

For example, 'giving' somebody a smile, hug, or flower can be considered deeds of greatness as they have greatly changed the situation (whatever that may have been) into one of appretiation of love.