Well, it's hardly copy/pasted. Yes there are quite a few similarities between the stories, but who's to say they didn't just come up with something they thought was original? I wrote an entire twenty-five-page thesis in University and it turned out almost everything I wrote was similar to a book written in 1984 that I'd never heard of.
And at any rate, the set pieces, characters, and all of the nuances to Mass Effect aren't plagiarised, and the story is told in a manner that differentiates it from this other work.
I'm not denying similarities, but if something with similarities to older stories was considered plagiarism, Star Wars, Indiana Jones, and plenty of other works would have never been made.
ONE MORE THING!
I'd actually be glad if a story had clear elements of something else, but wasn't a remake. That way it isn't shackled to the existing story, and can progress as the writers want.