Okay, here is my idea:
Humans are mechanic, aliens are organic.
The problem with this is that the Overmind isn't as organic as the Reactor is mechanic.
Then I was thinking and found a simple way to bring more life to the Overmind.
Then I modeled a demo model of it with a few variations, just to show you my idea.

Yes, the main modification is that the Overmind has a big eye.
There could be some interesting animations to it also, like when it is being built its eye is shut but when it has awaken it opens its eye.
And maybe if it is possible build in a tracker to make him stare at humans.
It would be so cool and creepy also.
Well then... what do you think?[/img]