In Mass Effect you discover the evil robots from beyond the cold, empty intergalatic space just come every now and then and kill everything in their way. When you ask "Why?" the answer the games gives you is "Who cares?", and it is both implied and said they are alien and old and uncomprehensible for us simple mortals.
This seemed to me like a try to pull a "Shivan". The Shivan are the "Evil Aliens" in the Freespace games: Basicly they appear out of nowhere when a civilization has reached a certain level of development and send them the way of the Dodo. They are alien, ancient, and uncomprehensible for us simple mortals. And even the way to defeat them is found in the ruins of the last civilization they turned to ashes, a way this civilization found when it was already too late for them to do fuck all. Sounds familiar?
The Freespace games, however, did it well. The Shivans ARE mysterious, alien, and uncomprehensible. They do not go around doing the "Mwahaha" number - They do not speak, they do not brag, they do not create personality cults. Some groups DO create personality cults around them, the Hammer of Light being the most prominent example, but the Shivans themselves do not care. They just go around happily burning planets and killing fleets. In the second game, though, they do actually comunicate with "us", but neither the player nor the alliance ever get to know WHAT they said, since the one they comunicated with was an admiral gone far beyond "rogue".
More so, in the second one they aren't even trying to genocide the Alliance. In fact, to this day no one knows what the fuck they were trying to do. They just sort of came and we were in the way, so they fucked us up the ass and then went their own way while having such a mamoth fleet they could have just steamrolled the entire alliance five times over with little casualties.
It doesn't sound like much when i write it, but in the games it is masterfully done. You feel you are fighting an alien, uncomprehensible, almost unstopable enemy in an uphill battle you can't even dream of winning once and for all. The fact that in freespace you a just some random pilot trying to do your best and not the hero upon whose shoulders the fate of the universe rests helps to get and keep that feeling. The first battles against them even have you in deep shit, with your ship not being able to even scratch the painting of their most basic fighters, and through both games most battles are either defensive ones, damage control ones, or let's win time ones. You never feel you have the upper hand, nor that you are facing a fair fight. The alliance is fucked and you know it the entire time, the entire war is about survival and is taking a heavy toll.
When i was playing Mass Effect the constant feeling, specially at the end, was "They tried to pull some Shivans out of their asses and failed miserably". Maybe it is just me, but it seems almost the same concept done with far less taste and style and then given to some really bad writers. It never had the urgency, the fear, the uphill battle, the part about winning time. Even at the end of Mass Effect, when it is implied all this have just begun, it is not menacing. We won, and what we lost? Zero. We even WON things.
Maybe it is the "trilogy" idiocy, but well... So far the thing is pretty ridiculous.