The biggest one for me is that FFV's story improved tremendously for me on a second playthrough. In fact, the older I get the more I appreciate that game, to the extent where it's probably my second favourite in the series now (after FFVI), or at least tied with FFIX for that honour.

Most of the other games haven't changed much in my rankings of how good they are since I played them, although the Compilation of FFVII has probably lowered my enjoyment of FFVII a lot.