Final Fantasy XIII is a pretty divisive game. There's the group which despises it and firmly believes it to be the death knell of the entire franchise, and there's the (admittedly far smaller) camp which sees it for what it is: an interesting JRPG which breaks the formulaic methodology of the past entries (something which Final Fantasy XII was lauded for) and does some kind of interesting things with its story, and some even more unique things with its combat. I'm going to attempt explain why the latter has some merit to its argument, and why FFXIII isn't the abominable blight on the series that so many think it is.
I'm gonna break it down into three categories in three different blog posts: Combat, Character Progression, and Story.
Though it may not look it in screenshots, the combat in XIII is a stark departure from previous entries. Instead of the traditional ATB, it instead utilizes a fully real-time system in which the player still chooses abilities and attacks like a more traditional JRPG, but in which enemies and players can potentially be using abilities simultaneously.
Defeating enemies entails more than just "attack it until it's dead;" XIII employs a system called "chain combos" in which the player attempts to fill up that bar (known as the "Chain Gauge") in the top-right of the screen, which "staggers" the enemy and causes them to take drastically increased damage from attacks. Certain classes are better at building up this meter than others, and ceasing attacks on an enemy causes the chain gauge to slowly whittle back down to nothing.
Character classes are broken down into "roles" - Medic, a healing class whose closest analogue would be White Mage; Ravager, a magic user who attempts to build up the chain gauge through quick assaults; Commando, a melee fighter who focuses on dealing as much damage as possible and slowing the decline of the chain gauge; Synergist, a magic role which casts buffs such as protect, shell, and haste on party members; Saboteur, who casts de-buffs on enemies; and Sentinel, who is essentially the "tank" of the game and possesses an extraordinary amount of HP and defense, and can even provoke enemies to attack him/her.
The player can switch party roles at any time using "Paradigm Shift," changing the entire party's roles simultaneously. It is herein where the depth of combat lies; without learning which roles to shift to and at which time to do so, combat becomes tedious, boring, and incredibly difficult.
For instance, the player may encounter an enemy which possesses extremely high HP and magic defense and is completely immune to being staggered, but is weak to the fire element and has low physical defense. In this case, the player would want to switch to a party containing two Commandos and a Synergist -- the Synergist gives the two Commandos Enfire (all attacks deal fire elemental damage) -- before switching to two Commandos and a Medic. Alternatively, the player could just use three Commandos, if he were confident enough in his abilities as to not need a healer. This kind of design theory applies to the entire game, and the combat ends up being more like a puzzle than a traditional JRPG system.
Defeating enemies is in itself rewarding -- each enemy possesses a "par time" for defeat, and killing an enemy or a group of enemies under par time increases your victory ranking, which leads to more experience and item drops. Items dropped from enemies include weapons, accessories, items useful for crafting, and items which serve no purpose other than to be sold for gil (the currency, which is not earned by simply defeating enemies).
The combat is indeed a far cry from "mindlessly press A until things die" that so many people seem to claim; there is a uniqueness to the depth that few JRPGs attain (fewer still post-PS2 era).
Next up: Character Progression.