Because we all like to nitpick (system related)

This is obviously just my opinion (probably add more later), but you may just agree

Useful Items and Abilities:
Curatives, Fangs (Red, White, Blue), Motes, Knot(s) of Rust (early), Cura (area), Curaja (area), Aero/Aeroga/Fira/Firaga/Blizzara/Blizzaga/Thundara/Thundaga (area), Immobilize (area/non-violent), Disable (area/non-violent), Break/Countdown (timed/indirect kill), Poison/Toxify/Sap (violent/interval/indirect kill), Oil (area/fire damage enhanced), Sleepga (area/non-violent), Dark/ra (area), Berserk/Silence (remove magic)

What's Missing:
Cure/Cura/Curaga/Curaja Motes: certain monsters can be fought with just melee but it's significantly harder to keep yourself healthy with just measures and items.
Trap Items: There are traps in the game. Only the main cast and occasional guest character can trigger these traps. Many traps bear effects which suggest they were man-made... for war? Why can more traps not be made for use in the field and why do monsters not trigger them?
Quick-Selection... the ability to change a spell Gambit with the press of a button. Final Fantasy VII gave access to "All" effect spells with the press of the R1 button. It was quick, efficient, and cost-effective. In XII, you must manually differ in the action menu between attacks that will effect one or a group which is really messed up as the more powerful attacks often are area-effect spells meaning you could potentially heal enemies with their element while drawing more attention to the currently isolated battle. Gambits are the only way provided in-game to reach specific abilities without scanning through an option screen. However, Gambits are only so specific. What happens when a Gambit is set to heal the party with Cura? The whole party is healed every time one party member takes damage regardless of the fact you've also placed a secondary healing Gambit meant to target a single ally. Without prioritizing the single-ally Gambit, the character continues to use Cura until they can no longer afford the MP. If the single-ally Gambit is prioritized, then the group-target Gambit is suddenly never used. As there is no Gambit for targeting a "group," there is no way to efficiently differ targets. As another example, what if a character was statused with Reverse. The group healing Cura would harm one of the party members, but there is no way to prevent the Gambit from activating when a single ally has met the requirement. The only way to ensure Gambits do an efficient job is to keep them in check. This means that for every new status ailment placed on the party, for every new monster that comes onto the screen, for every new situation, you must open your menu and rearrange the Gambits. Either Quick-Selection or more efficient Gambits would fix this problem.

Useful Gambits:
Foe: flying/(magic spell) or (technick), Ally: status = HP Critical/First Aid, Self: MP < 10%/Charge/Syphon, Ally: any/(curative magic: i.e. Blindna), Self: Libra, Foe: (pos.stat)/Dispel,

Useless or Obsolete Gambits:
Ally: Vaan/Ashe/Fran/Balthier/Basch/Penelo... if determined to target a particular party member, why not simply use Ally: party leader and then switch the current "party leader"?
Ally: MP < 20%-100%... honestly, what purpose do these serve? MP restoring items are hard to come by so assigning them to a Gambit would quickly drain your stock.


What's Missing:
Ally: any/curative... the ability to quickly differ between status effects without having to do so manually. With this Gambit, the caster would automatically cast Blindna on the Blind, Vox on the Silenced, Poisona on the Poisoned, etc.
Ally: reserve... actually, this should be a default sub-Gambit connected to Ally: any. Once the the allies onscreen have been seen to and there's nothing else to do (on the priority list), the main party should turn its attention to the reserve, restoring and curing. This way, the player doesn't need to manually target the reserve party.
AI Effectiveness: Gambits don't always lead to the right decisions being made. Characters may be smart enough to dispel negative effects rather than casting curative magic on a character who is unaffected; they may be smart enough not to continue casting buffering spells when they've already taken affect. The fact is that characters are not smart enough to realize an enemy no longer has an item to steal and after hundreds of fights they can't figure out an enemy is immune to a certain attack. The AI needs to have the ability to learn during the course of the game. Because of the fact that the Gambit system is a rather vague generalization of a more complex AI system, the characters need to be able to make smart decisions despite what is present on the Gambit list. For example, if there is a Gambit set up to cast Thundaga on the nearest visible enemy and there is a monster you've fought at least times which is immune to Thunder, the character AI should rationalize that casting Thundaga is really not a priority at the moment. If you really wanted to be ineffective or perhaps even heal the enemy, you could do something that stupid with a manual command.