I've got to say that in theory i love the leveling system. It is in fact a lot like the sphere grid. However it may have the crappiest UI of any Final Fantasy leveling system yet. They tried to make it artistic, which i suppose they succeeded at, but they also made it really confusing and awkward. I suppose that's something else that i may get used to after playing with it some more, but this isn't a problem i've had with other leveling systems before.
The basic usability complaint is that i have a tough time navigating it. So far at least i can't tell which crystals are glowing or not. I can tell which i've learned by looking at the "you've spent this many CP out of this many CP required" text. (Even though the numbers are a little too blurry to be sure of the exact amount in SD, i can at least tell if the first blur matches the second blur =) However that requires me to "mouse over" each skill to see if i've learned it or not yet. Maybe i'll get better at interpreting the glow later on.
My bigger concern is the fact that you've got a whole bunch of little circular sub-menus within each job, and each time you get to the edge of one little circle it jumps the entire screen over to the next little circle.
I seem to be heavily biased towards function over form. I certainly can appreciate a better form, but not at the expense of function. The same seems to apply at a bit more of a macro level as well. Back when FF10 came out, everyone else get a sense of wonder over the graphics. I admired the graphics, but my "OMG" moment was in response to opening up the sphere grid and seeing all those abilities i would get to learn. In FF13 everyone else starts the game and gets the sense of wonder from the graphics. I'm think the graphics are fine, but i get to the Crystarium menu and see a single circle with five or six skills on it to learn and say "That's it??!?" Intellectually i know that more stuff will get opened up to me later, but i can't see it now, so i don't get that visceral sense of wonder. I'll never be able to look down at a big chart of all the skills and see how much i've accomplished.
As an aside, the first thing the i remember learning about FF5, and the thing that convinced me i really wanted to import it, was seeing the chart of all the different jobs you could learn, complete with cute little anime depictions of the costumes for each of the jobs.
And this is going to be one of my big stupid gripes about FF13 (the other big one would probably be the missing music themes i supposed =) I know it's not that important, i know it doesn't really affect gameplay, but it bugs me. Why the hell did they change all the job names? After all this time slowly adding a couple jobs at a time why was this the point to throw them out? And from everything i've read it's not because of any gameplay reason, a Medic is still pretty much a White Mage. Which seems to me to mean that the only reason they did it was to be cool and try to appeal to the Modern Warfare 2 crowd, which bugs me out of all proportion to the actual affect on gameplay. Throwing out tradition because you've got something better to replace it with is one thing, just throwing it out in an attempt to be cool is something else.
Of course in my personal experience the effect has been that while the battle keeps on going in real time, with my losing points every second, i'm peering at the Paradigm menu's too small for SD text trying to figure out what the hell a "Ravager" equates to in normal job terms. (It turns out a Ravager is actually a Black Mage.) Like the problem with telling which skills i've learned or not, the direct gameplay affect is something i'll probably get over fairly quickly, but the aesthetic reverberations may stick with me for quite awhile.