They do have similar play mechanics and use basicly the same engine. So game play wise their the same, nothing else
Say you like a great game, thing FF7, and you finish the game, yet you winder to yourself, "Damn, I wish this game wasn't over yet" and you really want more of the action then you look for other games just like that game you enjoyed so much and play that instead. It also offers a new variety of things which the other game may never have. It's just a way to enjoy something you love, but in different way even if they are kinda similar.Why is everybody so happy about these games?? I mean FFA, Tactics Ogre, and Onimusa Tactics are exactly the same game.