I liked what Chris bring to ME franchise in general (which is, basically, "hard" SF aspect, attention to details and organic explanations instead of magic BS). What made ME special for me was not the plot itself (full of holes and basically Jesus Saves the World) and not only the characters (ME1 was actually rather light on interactions compared to most Bioware games) but the verisimilitude of the world and the believability of the science stuff. He's the one who wrote the codex and the planet descriptions, and THAT is what really made ME shines.
I'm pretty sure most of the idiotic stuff in ME, he was no part of it.
I didn't like the retconning of Geth from "showing the danger of rogue AI" to "usual misunderstood monster" cliché. That being said, Geth and EDI depicted by Chris were leagues above those depicted without him. Chris depicted AI as AI, and not just as metallic humans, and THAT was something truly unique, which was entirely lost after he left.
Thank you, I've been saying this since before I even knew who wrote Legion's character. I'm a neurologist, not an AI programmer but the basic physical science underlying both an AI (once we make one) and a brain should be identical, and I've said it before here - Chris wrote Legion's description of the Geth in ME2 much like a neuroscientist would when describing the concept of an alien AI. His description of what the Geth were like was brilliant. I'm not sure if he has read any neuroscience, AI research, or just really good sci-fi on the subject, but I think he must of as there's no way he just pulled that all out of his head.
Interestingly enough, our most useful and successful predictive theory of consciousness, Integrated Information Theory, has been used to predict which types of hardware design could be used to create a true artificial intelligence. And if you ask the question - "is an individually sentient, but collectively sapient communal consciousness like the Geth allowed in nature" - the theory predicts that yes, you absolutely could create an artificial intelligence like this and it would function almost exactly like how L'Etoile describes the Geth.
I've been meaning to write a blog article on that or something, as it is fascinating to me. But yeah, Chris is either a genius or just wrote an incredibly plausible background for the Geth out of pure chance.