I personally will enjoy playing BLU, and I especially love the way they implemented the Blue Magic.
It appears you may be able to set your magic on the fly, as it imposes the restriction that the BLU can't cast magic for 1 minute after you set it. If it was mog house only, you wouldn't need that restriction >:)
That'll open up to a lot more possibilities in the job class.
The only thing I can see sucking, is trying to get all the abilities you can. You'll have to lvl from 1-7 in all starter areas, 7-10 in all the starter dungeons, 10-20ish in bubu, valkurm, intermediate zones, korrolloka, etc etc. It'll be a chore to get as many abilities as you can before you grow too high of a level for them.
luckily once you would hit 55+, all/most mobs are ep+ to 75, so that'll make life easier and you can cruise xp more without worry. Until that point tho, you need to have diverse pt locations to be able to learn all the magic you can. :o