Yep. The power of the power fantasy. I know fully what it is, and I ride it into the ground like flaming chicken.
Shepard is even more irreplaceable than the Crucible.
I'm going to use that power to be a bit corrupt.
I don't usually have a problem with power fantasies in fiction, the problem is that Bioware took it to the extreme. Power fantasies in video games these days are usually limited to allowing the player to mow dow loads of enemies, have any woman they want, and pretty much do anything they want, making them feel like badass in the process, but they will never, not ever, constantly tell the player that no one in the world is as badass as them.
Even in RPG's, where the concept of the chosen one is prevalent, PC's are still surrounded by competent characters who will help teach you but also call you out on your BS if you do something stupid. This is where Mass Effect fails, everyone else is made to look incompetent in relation to the almighty Shepard, Shepard is never wrong, every choice he makes is the right one and anyone who calls you out on your BS just happens to be killable.
NPC's will constantly be kissing your ass, telling you how awesome you are, how you're the light in the dark(worst line in the game), how no one else can do what you do, that the only reason they have a chance of winning is because of you etc, it's insulting. Other RPG's at least have reasons for why you're so special, like Skyrim and Morrowind with the Dragonborn and Neravarine respectively, Shepard has none of that.
Honestly, I hope Bioware realise that their entire fan base is not built up of lonely nerds who need a video game to tell them how awesome they are in order to feel good about themselves, they should take a far more mature route with their future Mass Effect games.