Because of the name?Or lack thereof...
Well, you have two sides to choose whom which have separate storylines to follow. If that's not replay value, then I wonder what is? I'm also sure that you won't be able to find every secret in one playthrough.
you mean youve never finished Deus-Ex
I shall kneel before the Sacred Terrabyte of Gaming Goodness (hail the majestey) and pray to the gaming gods for your salvation