Completed as in beat the final boss or done all side-stuff?

For the former, all the ones I've played. That includes IV to X, X-2, XII, XIII and XIII-2.

For the latter, I have yet to do the optional dungeons in IV, V and VI.
Done everything in VII, VIII and IX (except getting Exc2), I have all Steam achievements for VII and most of them on VIII (except for things like Chocobo World and max Gil).
As for X, I have beaten all optional bosses, but I'm not really satisfied with it since I basically only copied strategies from the net.
X-2, got everything you could possibly get in that game.
XII, I never beat Yiazmat or Omega Mk. XII. Nor have I played IZJS.
Finally, I've platinum'd XIII and XIII-2.