FFVIII did quite a few things right. The big mistake was attempting to integrate the battle mechanics into the story. That and the facepalm inducing
We all grew up together and Edea was our caretaker, but then we forgot
plot twist. If they have to choose between taking the XIII path or the VIII path, I say VIII all the way.
If they would have a look at 3D FFs and took something out of each one: the atmosphere, feel of VII, the character design of VIII, the charm of IX, the battle system of X, the fantastic vast "overworld" of XII. Then, used XIII for comparison and changed anything that matched, it would potentially form the ultimate FF game.
The list of big mistakes FFVIII made include the following:
- Making the world setting so sparse you only encounter two major world powers and a handful of towns.
- The technological disparity between the two superpowers makes you wonder why any fucks are given for one of them.
- Flashbacks to a team of chucklefucks who don't do a damn thing worth mentioning for the time you flashback to them.
- Making the antagonist's big focus trying to figure out what the hell SeeD is (and TIME KOMPRESSION).
- Not making the other Sorceress the main antagonist (and I'm not talking about Edea).
- Making you cart around a team of nameless, faceless chucklefucks (with names and faces but "whatever" "....").
- Saddling you with the worst incarnation of the Final Fantasy female lead archetype ever created.
- Starting the game off in a Japanese High School setting.
- That's also a paramilitary organization that fulfills mercenary contracts between the one active world power and a few towns.
- That only employ Japanese highschoolers to fulfill said mercenary contracts.
- Armed only with memory wiping creatures and a couple crappy weapons.
- And are told nothing useful because, aside from the main character, they're just a distraction for the real A-Team.
- And their plot macguffin princess which is the one that actually matters to the main antagonist.
But I guess the tl;dr of that list is that you shouldn't make the entire world literally revolve your main character and make his romantic side plot the game's real plot.
Also trying to cobble together a game from all those parts from previous 3D FF games is a recipe for disaster for the following reasons:
- FFXII's world is too vast for X's battle system (especially with random encounters).
- And too deserty to capture VII's overworld's feel.
- VIII's character designs are too mundane and stick in the mud for the essentric and cartoony world of IX.
- Or alternatively, try to imagine what Quina might look like in a less deformed style.
- Also have fun trying to fit charm into places like VII's Sector 6, Shinra Building, and Gold Sauser's desert prison area.
- And you can't use a Sephiroth clone (XIII-2), a Robo God (XIII-1), random encounters (XIII-2), or on-map encounters (XIII-1).
- Plus you can't use a (loosely) interconnected map (XIII-1), time travel (XIII-2), a clam lands (XIII-1), or a casino (XIII-2).
- Also Chocobos, Moogles, shops at save points, towns intergrated into the world map, gunblades, motorcycles, and dyson spheres are also out.
- Nor are Pokemon/SMT recruitable monsters allowed.
- In fact, a lot of what FFs XIII-1 and XIII-2 do are done a lot by other FF games and it would be kind of a bad idea to exocise everything.
The tl;dr is that just saying "I want this, and this, and this, and this, but nothing that has to do with this in my perfect game." is a bad way to design games.