If there's one thing this novel will be remembered for, besides the Canon Defilement, it's almost certainly Kai Leng:
Kai Leng breaks into Anderson's apartment to bug the place... and then stops to eat Anderson's cereal. Because he's an "adrenaline junkie". Kai Leng: CerealKiller! This was so funny, and yet fitting into his character, that many on the BioWare forums agree that even if there is a revision, this is a part that should be left in.
Another example is when he's on a stakeout to catch Gillian. He's literally watching out for her through his sniper rifle scope, and the narration helpfully informs us that "just as he was about to pee in the vase he had selected for that purpose, something happened". Not quite as memetic, but just as hilarious, especially because of "pee" being an Inherently Funny Word. That and the notion that Kai Leng likes to pee in vases. And not just any vase, a vase he specifically selected for that purpose.
Him using a sharpened toothbrush to kill Gillian should be horrifying. But he uses a sharpened toothbrush. And with the Citadel DLC pack, this makestwice that toothbrushes have had a major impact on the Mass Effect universe.