GCDs in FFXIV are longer than other games, 2.5s instead of the standard 1-1.5 seconds. However, FFXIV expects every class to hit a button each GCD in their main rotation.
For classes with instant attacks, like melee classes, this usually means that the actual attack takes up a slice of that GCD, and gives the player a small amount of time to move their character. This is important, because melee characters need to move between the back and flank of the target during the rotation.
However, classes in FFXIV also have a set of off-GCD abilities. Because of the way animations work, you can effectively use one off-GCD ability per GCD.
So each GCD can have a max of two abilities. You're guaranteed to press at least one, the main rotation ability, but only some GCDs will have the second ability used.
You could model this with two GCDs (though I suppose they technically aren't "global" anymore). Some abilities trigger GCD 1, others trigger GCD 2. There are no empty GCDs in track 1, but there are some in track 2.
I think this method is pretty good. You get into the rhythm of your main rotation, each ability coming 2.5s after the last. But there's lots of empty space to throw in cooldowns and specials. As well, you can't trigger all your cooldowns at once, but have to space them out. The biggest downside is that classes can seem very slow at early levels, where you only have track 1 abilities.
On the whole though, I do like FFXIV's approach to GCDs. I especially like the longer GCDs. It slows the game down a bit, makes it a touch more forgiving. I have never been a fan of the way Haste speeds up the game by messing with the GCD.