And what are the core issues of FF1? Time paradox! Actually there really is none.
The Final Fantasy games don't try their hand at more indepth story telling until Bartz and usually just presents big villains who try to pull off some big gambit and either succeed or fail.
Some seem really interesting. Cloud of Darkness for example is a very interesting villain in concept and could be expanded, especially given how the plot goes, upon. Yet the game doesn't attempt this because it is an intentional retread of the first game where you step up to become the Warriors of Light, but against a villain who is beyond such.
Where Bartz presents the exact same villain as the Cloud of Darkness (honestly they are carbon copies)... but where the focus of the game is on the personal relationship between the characters as well as to the previous group of adventurers. With a sense of generation.
-Honestly the similarities between that game and Onion Knights is staggering... Except I think Bartz' game is better in everyway, except a bit TOO obvious.
I will say that what most people don't understand about a lot of Final Fantasy villains is that a lot of them are meant to be incarnate versions of concepts. Cloud of Darkness being the first in my mind.
Here are a few I feel are that:
FF9: Necrid is meant to be the living embodiment of the struggles between Kuja and Zidane and the naturally conclusion of these struggles (the end of the universe)
FF10: False Religion in general. The last boss is so easy because you already saw through the lies, it holds no more power over you.
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I would also like to clarify that the "childish" accusation tends to be more "Console games are made for children and thus are nothing more than "press the button to win" games with absolutley no depth. THey don't have any other option, because they don't have enough buttons."
That is because they use Final Fantasy as the template... and Final Fantasy is supposed to be the more casual RPG. It is why Final Fantasy Tactics is so much easier and 2-dimensional then Tactics Ogre, and why Final Fantasy Tactics Advance is even more simplistic then that.
If they stepped outside of that... AND outside Dragon Quest (which is for a younger generation) And out YS... and you know a lot of JRPGs.
They might see differently.
That and a LOT of JRPGs are marketed towards children (to the extent where they redo the art in the booklet to change things)... and most of the Computer RPGs you are referring to are marketed towards adult