I've played every numbered Final Fantasy including their respective sequels/prequels and a few spin-offs here and there. I haven't finished FFI-III since I got to those later in life and couldn't stand the sluggish pace of strict turn-based gameplay. Had I played through them when they came out I might have appreciated them more. I can't really say the game mechanics evolved as much as they were iterated upon post Final Fantasy IV. It wasn't really until they finally dropped Sakaguchi and Uematsu post FFIX that I really saw the series start to evolve in different ways.

FFX going linear and introducing the CTB system with the sequel revisiting a world rebuilt, while FFXI went straight up MMO, with FFXII doing interesting things with the story and making the world feel massive, then FFXIII giving the battle system a 5-hour energy drink and focusing on flawed characters and a generally bleak storyline. People will bitch and moan about which entry is the best and everything after it is crap, but watching the series evolve over the past ten years has been pretty exciting and I've loved every bit of it. What with Japanese development FINALLY catching up to next-gen development, it'll be interesting to see what they do with future entries in the series after Bioware and Bethesda have entered the console arena.

Sort of a sidebar to the actual topic, but meh.

On that note however, why do people seem to think FFVersusXIII, a game that at this point seems to be nothing but vaporware, is going to be the game to "revive the glory" of the Final Fantasy series anyway?