So...
The theory behind why aliens would be very similar in anatomy to humans is basically evolutionary convergence. As we have a very limited understanding of complex organism, specifically those that aren't very similar to us, it stands to reason that similar environmental influences would produce very similar biological diversity. Two organisms, experiencing roughly the same factors, will favor the same traits. As far as just being green skinned humans, that's a cheap way to reskin a model rather than develop a new one.
As far as this game... meh.
My initial reaction is that they just showed us all the playable planets in the base game, and anything extra will be paid for DLC. Honestly, Bioware pissed away all the good will of their releases (starting with Jade Empire) when they spent the better part of a decade lying to their customers. Yes, they eventually "fixed" the Mass Effect ending. My problem is that all their recent trends lead me to believe that this will be another mediocre game. Mediocrity, with the stink of Origin only, means I'm going to have to pass on this game until it demonstrates that it has to be played.