Originality is....to a certain extent....a myth.
Do you really think most popular works are truly original?
No, all of them have inspirations from other works.
Even Shakespeare adapted his works from older, common stories, or so I'm told, and in turn, many works from derived from his ideas.
But I can assure you I haven't seen anyone really pull off this idea before, these two other games are quite simply the closet I've ever seen come close to that, and they certainly have a lot that could be learned from. Thus, there's still some originality, but with plenty of inspiration from good ideas.
And if doing this is so wrong, why is it hollywood makes so many sequels and such, and they sell....really well?
Execution by a good director is of course critical too (often what makes so many other movies fail.), but that's the point, it matters more how you do it, more then it matters what you do.....as long as it's not a half-baked idea. And I've thought out a lot more to this idea then your aware, it's not half-baked.