Actually, I'd like to bitch.
ME1 and 2 and most of 3 are pretty damn hard in terms of their science fiction. The only unrealistic element, really, is Element Zero and to a lesser extent, the effect Eezo has on living organisms, see Biotics. But they take that ONE plotonium element and expand it to encompass everything in the game.
I mean, for example, the red-lazor of death fired by Sovereign and Harbinger are not actually lasers. They're massive amounts of ferrous metals accelerated using a mass effect field and a powerful electromagnet, shot at ALMOST the speed of light at an enemy ship. It looks like a beam because the material is somewhat diffuse, but it hits harder than fifty nuclear bombs because...you know, physics are a bitch that way.
The machine-organic hybrids are created through obvious instrumentation: The dragon's teeth or the Collector facility, which are presumably using some kind of nanobot, cybernetic synthesis to transform people like this.
I suppose you could say that the Crucible uses nanotechnology to do this...transmitted at faster than the speed of light by some mass effect field trickery, but it still strikes me as a bit of a stretch, considering how complex and complete your knowledge of the target lifeform has to be.
I mean, I always figured that's why it took so long for the Reapers to start using non-human husks: Because their initial contacts and collections in this current cycle were humans (I mean, it's not like Saren was going to be feeding them non-humans, considering how much the dude hated humanity), they could work on them efficiently, while the other races needed more extended contact: They hit the Batarians next, then the Turians, and finally, the Asari, and that's the order in which the husks of those races started to show up.
But there are literally thousands, if not tens of thousands, of races that the Reapers and the Crucible would not have had any contact with.
And this is all being extraordinarily generous and saying that the nanobot disperasal pattern would even work, and that the heat waste produced by bazillion little chemical factories working to completely alter a body at the molecular level wouldn't reduce everyone to bubbling slag.
It...just strikes me as a weeeee bit of a stretch.
EDIT: Here's how I'd have re-written synthesis.
Shepard's mind and the A.I of the Crucible fuse into a seed A.I, which guides the galaxy's synthetic and organic life-forms through a gradual uplift to a technological singularity. It takes longer, but it has the same "sacrifice to create a new world" thing.
Also, needs slightly less space magic.