Well Tali is going to look rather human like; anyways in mass effect 2 a lot of screen shots show the outline of her face, if you have a quick eye you can notice them through out the game specially during her loyality mission.
So she has a very human like nose, chin and cheek bones. While you don't see any color or details you do see the out of her face structure specialy when she turns away from the camera.
Also they made a low detail image of her face inside the helmet on the computer you can alter the camera to zoom in on her helmet so close that you can see the face its self.
also in ME 1 i can practically see her face.
She does have rather human like features, sorry to break it to you spacemarines.
She's very human like, the most they can really change would be the skin color and eye shape.
Also I think bioware made her helmet semi transparent to give people little teases to what she does look like. I wouldn't be surprised they had the face made for a while now.