Finally got my hands on the demo tonight, and played through both modes a few times. Since I'm being asked for impressions by a few friends, and since there still seems to be a bit of confusion about how a few things work, I figured I'd just cover it all in this post:
Wait Mode: for thinking players.
"Wait Mode" works a bit differently here than in previous Final Fantasy titles. Now, instead of only pausing the ATB bars while you're tinkering around in the sub-menus (magic, item, etc), things
completely freeze the minute you open the command menu via the "X" button. ATB bars (for both your party and your enemies), attack animations, background effects -- it all freezes completely. Closest comparison I can think of is the Grandia games, when prompted for a command input, or the KotOR titles when you hit the "White" button.
Basically, this gives you an infinite amount of time to plan out your attacks, as
absolutely nothing will progress until you either pick a command, or exit the menu. You can also open the command menu
at any time during the quest, even if all of your characters are presently attacking... and, if timed correctly, you can even queue up a second command for a character. In result, you can set your own pace here, even more-so than you could in any other previous ATB-governed FF.
Other than that, combat works rather similar to that in FFXI. Once engaged, you and your party members will continue to do a base "Attack" action everytime your ATB bar fills, until told to do otherwise. When opening the menu, you're given the typical command list for the character you're currently controlling (Attack, Magic, Summon, Item, etc... you know the drill), along with the option to hit left or right on the D-Pad to cycle between your party members' command lists (ala Chrono Trigger).
Active Mode: for thrill-seekers.
"Active Mode" is pretty much the polar opposite.
Absolutely nothing you do, save for summoning Espers, pauses the action. Instead, everything continues as if it was proceeding in real-time, so much so that I doubt most people will even realize that it's still a turn-based system.

Given that, this is a much more frantic mode, as you're having to dive through the menus to pick spells and items on the fly, while still trying to keep your eye on the action.
Other than that, pretty much everything else works the same way here as it does in "Wait Mode," save for one thing: queuing up attacks is
much easier.
To explain what I mean:
Once your ATB bar fills, your character is prompted to carry out whatever command s/he was told to do, and the word "ACTION" appears below the bar. Once this appears, even if your character hasn't executed the action yet, you're able to queue up a second command, which makes the word "NEXT" appear beside that character's ATB bar. With this, once your character is finished executing it's current command, it will automatically start charging up for that second action in the queue.
What makes this easier in "Active Mode" is that while you're fiddling around in the menus, the action doesn't stop. For instance, say you have Fran set to cast "Cure" on Balthier. Then, while her ATB bar is charging up, you select "Cure" again and hover the cursor above Ashe. As soon as her ATB bar fills and the word "ACTION" appears, you hit X to select the target (Ashe), entering the second "Cure" command in the "NEXT" queue. The result is a sort of "chain-casting" effect, as once that first "Cure" spell is fired off, she'll instantly begin executing the next.
While the queue option is available in "Wait Mode," as well, it's impossible to do the above as all of the ATB bars freeze the second you open the menu.
Getting away from the "Wait" & "Active" thing here, there are a few other systems present in the demo that aren't getting mentioned very often:
Aggro Schemes
Much like Final Fantasy XI, certain enemies simply don't wait to get attacked before being hostile towards you. And, much like in that game, there are multiple ways in which they aggro, indicated in the demo by the color of the enemy's HP meter/bar:
• Green => No Aggro
Any enemy with a Green HP meter isn't hostile at all, and will go about it's business until you engage it. An example in the demo is the Mandragora.
• Yellow => Magic Aggro
Any enemy with a Yellow HP meter isn't hostile at all, until you manually engage it, or cast a spell near it. This includes White or Green magic, as
any type of spell cast will gain the enemy's attention. An example in the demo is the Bomb.
• Red => Sight Aggro
Any enemy with a Red HP meter is completely hostile, and if you enter their range of sight, they won't hesitate to attack you. This aggro type seems to be the most prevelant, if the demo is anything to go by. An example in the demo is the Sleipnir.
It's hard to say if there will be anymore types in the final game, but there is one missing that was also present in Final Fantasy XI: Sound Aggro. It's possible that this type will be present, along with a variety of spells (likely Green Magic) or abilities that allow you to avoid being detected by Sight, Sound, etc. We'll just have to wait and see.
Gambits
"Gambits" are pretty much FFXII's "AI Routines," only instead of being a bullet-point on an options menu, they're something you equip. It's hard to say how customizable these will end up being in the final release, but already in the demo you can see the effects of different types.
For instance, in "Wait Mode," the Gambits tell your party members to instantly attack whichever enemies you engage, hostile or not. So, the second you target an enemy (with the "Attack" action, at least), your allies will follow your lead and do exactly the same.
Meanwhile, in "Active Mode," the Gambits tell your party members to only engage enemies that aggro the party. In result, when you engage a non-hostile enemy, your party members basically sit around twiddling their thumbs until your attack connects, and the targeted enemy aggros the party. Essentially, it wastes a turn. :\ If a hostile enemy aggros the party right-off, however, they'll instantly engage it and start charging up their attacks.
There are many other effects present in the demo from the Gambits system, like focusing on the enemy the Party Leader (ie: who you're controlling) targets, or casting Cure spells to keep party HP above a certain level, to auto-attacking after finishing whichever command they were prompted to perform, etc etc.
Also, you can quickly and easily toggle Gambits On & Off via the basic command menu, to essentially take full control of your party on-the-fly. This is already beneficial in the demo when you're running by Bombs with low HP, as with the Gambits turned on, Fran will be attempting to cast curative magic on your party, leading to Bomb aggro. Oops!
Summons
While the game has gone back to using the FFVI term for summons, "Espers," the summon system works more like Final Fantasy XI's than anything. For instance, once summoned, the Esper replaces your allies, and runs around as an uncontrollable party member. In result, the summoner is the only controllable character left, and is thus made your "Party Leader," even if you were controlling somebody else prior to the summoning.
Other than that, Espers are basically a uber-party member, following along behind you and executing some really brutal attacks (killing some enemies in a single hit). Difference from FFXI here is that they don't slowly tick down your MP meter, and instead work off a timer, indicated by a few circles that slowly disappear in the lower right-hand corner. Once the timer ticks down completely, the summon executes one final, screen-clearing attack, and then disappears.
Those belly-aching for "dazzling spell effects" will be happy to know that all of the action pauses while both summoning an Esper, and during it's final, screen-clearing attack. These sequences are very pretty, and last a good amount of time (I swear the screen-clearing attack lasted a minute or so...), to the point of being actually a bit over-done... which seems to be what you guys are looking for.
With all of the explanations out of the way, my view on things:
I've never been one to think that Final Fantasy needed to "change," or "evolve." I've always thought that the series has changed enough with each iteration, and that there was simply no need to go and reinvent the wheel with the series. Final Fantasy has always worked, and there was never anything broken, so why fix it? ...But even going into this with that mindset, I can't help but sit here and think:
I love the direction this took.
Even just looking at the battle system, I think the inclusion of the "Wait Mode" will go an awful long way to keeping series' veterans, whom are attached to the traditional "Dick around in the menus, no harm, no foul." style of play, quite happy. They get their traditional, turn-based set-up, and the game didn't have to sacrifice anything from the "Active Mode" side to offer it.
That said, I'm not much of a fan of "Wait Mode," as while it gives you infinite prep-time to plan things out, I think it simply keeps the action bogged down too much. "Active Mode" all the way for me, as I just love everything being so snappy. And I love being able to cursor hover to chain-cast, or change actions mid-charge without having to have the game freeze the action on me, etc etc.
Even putting that aspect aside, the concept of combining Final Fantasy XI/MMO elements into a single-player title had me a little skeptical at times, making me wonder just
how much it'd play like FFXI, or how much of the grind, downtime, etc would make it into the game. But I'm happy to say that absolutely none of the downsides of that game are present here. Instead, they've only carried over things that help make the game a deeper experience, like the aggro schemes, the experience chains, and so on and so forth.
All of that said, I still don't think this is so much an "evolution" of the series, as it is just a great alternative direction for the series to go in. I think they've pretty much aced the combination of styles here, and I can't wait for the final release, especially to see how much more in-depth the new gameplay systems go...
...In other words: I'm sold.
