Kael pretty much nailed it, and Jaxon has a valid statement about ME2's plot resembling swiss cheese.
Why do most of the Reapers we’ve seen so far have similar insect-like appearances? The human Reaper looked different, but otherwise it seems like the Reapers mainly build themselves out of bugs. Is that correct?
The exterior of the Reapers does follow a similar pattern, an efficient design for the purpose they were created for. However each Reaper is created from a unique species, and as we saw at the end of Mass Effect 2, the core of each Reaper is designed in the likeness of that species.
I for one welcome our cuddlefish overlords.
Also, Portal 2 is pretty much the greatest thing ever.