I like the Mass Effect games a lot, but I'm actually pretty disappointed with the romance subplot. I remember playing the first game and, I don't know what I was expecting, but after all those conversations your reward was a sex cutscene. I was like, "That's it?" Apparently so. And it's not like the character you choose treats you any different in the missions, or there is any difference in the story. The same goes for Mass Effect 2: I played through the romantic subplot and was once more rewarded with a (somewhat less racy) sex scene. *Sigh* And it's sad, 'cause the romantic options in the sequel were better than in the first game. And in a game where the consequences of the choices you make are one of the biggest rewards in the gameplay, it's sad that one of the most important choices you make does not matter outside of a few seconds of racy CG sexuality.
In general, I tend to shrug my shoulders at the idea of sex in video games. I figure it's a part of life, and it sells, so it's going to be featured in games more and more. I like that the scenes in the Mass Effect games are optional, so if you don't want to have that happen, you don't have to. But the sex scenes in games are probably not going to portray the kind of Biblical sexuality you might want as a Christian. (Commander Shepard does not marry the object of his affection before they do it.) Video games are going to portray sexuality the same way as the rest of secular entertainment, like movies and television. The only difference is the interactivity of games. You decide whether or not to have your virtual character sleep with this virtual person. And, while it is "only a game" and I don't think your virtual choices are necessarily reflective of your heart (otherwise Christians would probably all go the Paragon route, right?), I think you've got to be aware. Just know that this is the voice of the World speaking to you, telling you what is okay in the realm of sexuality. God has a very different opinion.
Also, I have a feeling that this kind of insertion of sex into video games is going to eventually lead to mainstream video games having scenes that are straight up pornography. If the purpose of the game, or scenes in the game, is to appeal to the player's lust, then it's time to go play something else.