To expand upon SerenityPD's point, the similarity between the various Final Fantasy titles is actually far smaller than that between most completely unrelated FPS games. They have wildly varying settings, characters, item/battle systems and stories. Most FPS are either generic sci-fi, WW2 or some other (recent) historic war. Think about it.
(And now I made a fool of myself like czekon by posting about a subject I know next to nothing about, namely FPS. Let's see if my point is as easy to disprove)
(And now I made a fool of myself like czekon by posting about a subject I know next to nothing about, namely FPS. Let's see if my point is as easy to disprove)