Hm, regarding Leviathan... You can look at that as an answer to why the Reapers did what they did, but I think it's strong evidence that not all AI would act as the Reapers acted. In fact, you could even consider the possibility that maybe they did what they did to protect organic life from the Leviathans. Basically, my "feel" for the Leviathans was that they created a tool that ended up being a whole lot like them, minus any emotion (though that's arguable, too). The Reapers use other sentients in the same way that the Leviathans did. They actually groom other species to grow along certain paths, just for the sake of being harvested. So to me, the whole argument that the cycle either has to continue or everyone has to undergo synthesis still falls flat. And, I also wonder if the Leviathans would be the next big threat in the ME-verse. Before I thought it would most likely be the yahg. If they set a game in the future, I guess I'll be glad I spared the krogan (though I doubt they'll have import games, if they ever do).
But back to Garrus. Omega should be interesting for him, yes. Maybe Sidonis will be there, since he appears nowhere in the base game.
Speaking of Omega, the books pretty much inform us that it's a den of hedonism and depravity. I'm pretty sure Garrus wouldn't have done recreational drugs, not when he was out shooting the drug dealers. But sex? I'm thinking he probably indulged frequently, as long as he could avoid being with a slave etc. He wasn't shy about talking about buying Grunt a few dances back in ME2. Which, well, to me, it makes me wonder if he'd been that promiscuous, would he have trouble forming an actual lasting bond with Shepard, Tali, or anyone else? Granted, he's not human, but recent research on human psychology has revealed that the more partners you have/have had, the harder it is for you to settle down with just one person. To me, that makes perfect sense--why settle for one when you can get all of the benefits from a wide variety of people and not have to deal with the hardships of maintaining an actual relationship?
And yet, did he have time to pursue even casual sex on Omega, while busy making himself into Omega's Most Wanted?
And, back to the old topic of whether Garrus's behavior is too human... Yes, I agree that he should have had some more alien gestures. However, I never got the impression any of the human gestures he used in the romance were familiar to him. I felt like he was learning about kissing (possibly because he'd only done the forehead touching in the past and Shepard was showing him something new). And he apparently learned about handshakes and dipsmooches from Joker's porn vids (creepily enough).
So ask yourselves, why was it so important to Garrus that he find a human way to express romantic interest in Shepard, rather than going about it however turians do? My thought is that it's precisely because he wanted to express a romantic interest, as in he wanted to make it clear that he wanted to be more than her friend with benefits, that he was interested in being her boyfriend. If he tried to show that interest in a turian way, she might not understand it--and he, of course, can't "read" her either, to know what she wants from him--if it's just sex, then he wants to convince her to consider more. And let's be honest, Shepard doesn't really make it clear what she wants until Garrus finally asks if she wants an exclusive relationship with him. So, my take on it is that in essence, this is Garrus's way of being more aggressive/involved in the romance--something a lot of people wanted, since it was entirely Shepard pushing the romance before. And it also shows that yes, this is something he wants. He wants it enough that he will go out of his way to learn ways of expressing affection that are quite literally alien to him. Pressured into it or not, he ain't complainin', folks.
But, take it with a grain of salt because I tend to overthink things, and I'm trying to write a fic which means I'm overthinking things even more than usual. Sort of. If I ever remember to open the document again when it isn't super-late at night.