A complete list of in-game flaws including many that make it impossible to finish without restarting from the beginning.
BATTLE and SYSTEM
I'd like to fight Black Cloaks. And Sapphire.
Mirror's Edge action: 1st-person (3rd-person? 1st/3rd-person?) interface.
Crisis Core's materia merge should be in VII. DoC's accesory and weapon parts system too.
You should be able to forge the First Tsurugi after collecting the Hardedge, Ragnarok, Force Stealer, Murakumo, and Apocalypse (maybe at the Weapon Seller outside Gongaga). The First Tsurugi could have three slots (two linked) worth triple AP growth and be second in strength only to Ultima and obtaining it could unlock a scene on ground approach to Midgar in which Cloud places the Buster Sword in dedication to Zack.
GRAFIX
Opening Screen
In Battle
Cloud in Action
Super-realistically deformed
Sephy in Action
Sephy-deformed
Super-FMV-Deformed
STORY-DRIVEN SIDEQUESTS
Quest to cure Seto. Bugenhagen's past. Vincent's story for those who refuse to pick up DoC. Yuffie's for those who refuse to pick up Crisis Core.
LIMIT BREAKS
More enemies (particularly SOLDIER 3rd-1st) should have LIMIT breaks.
Level 4 process should be deeper if slightly.
Omnislash as a prize. Why? What does that mean?
Tifa gets hers from Zangan's letter... should be a flashback of Zangan trying to teach her the technique only to find she was not yet ready.
Barret's is acquired from N.Corel but there's no way that can be "learned". Maybe it's some kind of rocket fuel attachment. To be perfectly honest, though I'd like an explanation as to how the hell Barret uses Satellite Beam.
Aerith's makes no sense at all in that it can be acquired multiple times from the "weapon seller" outside Gongaga (a glitch which should be repaired)...
Yuffie earns hers from her father via combat: makes perfect sense.
Vincent gets his from Lucrecia in that hidden cave: also easily explained.
Cid's is found in the crashed Gelnika: could just say it's a manual for attaching armaments to ships.
Nanaki: it's pretty weird that he obtains his from the optional battle with Lost Number preceding one's potentially recruiting Vincent.
EXTRAS
Defeating Zolom before entering the Mythril Cave for the first time should warrant a slightly different dialogue.
Cloud should have at least a high enough defense in the flashbacks to not die after one hit from anything (even that damned dragon). Although it's neat to see Sephiroth randomly decide to revive Cloud, most of the time, Cloud just stays dead.
SOLDIER 3rd-1st Class's swords should be changed to the ones in Crisis Core, 'cause using cones is just weird.
I want Cloud to be able to obtain and wield a copy of Genesis' Rapier and a SOLDIER sword (the cone-looking things) as easter eggs.
ALTFITS
Cloud: MP (complete with "joke weapon" Rifle which he'd use like a sword), SOLDIER 1st-Class (only real difference being helmet and extra shoulderpad; requires SOLDIER sword to complete illusion), Ms. Cloud, Kingdom Hearts, Advent Children, Fighter (FFI), Warrior (FFI), Dark Knight
Barret: Sailor Suit, Advent Children, Heart of Monk (shirtless with long ponytail)
Tifa: Cowboy Getup, Advent Children, MP, Floozy, Rosa (FFIV)
Aerits: Before Crisis, Kingdom Hearts, MP, Pretty Woman, White Mage
Red XIII: Django (Ehrgeiz), MP (only visible in and out of battle during ShinRa boat event)
Yuffie: Sailor, Reporter, Thief (FFI), Ninja (FFI)
Cait Sith: MiniMog, ChocoJock (changes giant mog into a Chocobo), Reporter
Vincent: Turk, No Cape, DoC Beast (only affects Galean Beast LIMIT), DoC Chaos (only affects Chaos LIMIT), Red Mage (basically just Vincent with white hair), Raziel (Soul Reaver)
Cid: Advent Children, Cid Prime (FFII), Kain's Armor (FFIV), Solid Snake (lol)
Sephiroth: Kingdom Hearts (comes paired with Kingdom Hearts Cloud... non-playable)
Altfit that could potentially fit EITHER Cloud or Tifa: Aya Brea, lol