[quote=thewizardguy]
Gilgamesh values power above all, and believes all to be his property. He relishes being above all there is, and sees himself as factually superior. All is his domain.Iskandar lives to the fullest, and believes in being the greatest conqueror. He wishes to take all by force because he is simply that badass.Their mentalities are quite different.
[/quote]

He's talking about something Gen, the creator of Fate Zero, went off about. It's how Gilgamesh values objects while Iskander values people, and though their ego is the same what they place value in is different, hence their very different outlooks on the world.

It's less that they're same in personality, but same in the level of ego they have.