New unique locations for each of them, legendary quality/stats, and nearly all of them now have complete movesets. Details on each can be viewed either on Cymre's blog post or @patf0rd's google document.
In total there are 15 boss pets to defeat (I thought there were only 14, so one must have escaped me), and each one awards Fel-Touched Pet Supplies. There are only four new pets that drop from this reward bag so far, but my hope is that more will be added. Perhaps versions of the actual boss pets that we have to defeat? I'd love a Bleakclaw of my own! :3
I mean, four new pets out of 15 possible bags really feels uninspired, and it makes it difficult to believe it will be worth taking the time to travel to each legendary pet and completing the battle every single day. Dedicated collectors will definitely attempt it, but I can't see very many keeping up with the routine after a while. It just screams "burn out". If there were more shiny new pets/things to collect from the daily reward bags, that might add more incentive to do them all and continue doing them.
Going through and trying to find/defeat each one the other day on the PTR left me exhausted. I managed to find seven out of the 15 before throwing in the towel for the night. If it takes that long to travel to and complete all 15 dailies, I may just skip the majority of them and park alts at certain ones. Because ouch, it was time-consuming and frustrating.
Don't get me wrong, though. I think (and I hope) the travel time will be reduced now that the location of every boss pet has been revealed, and an efficient route will probably be plotted out by testers. Plus, once further testing is done on the PTR, the community will create ideas and suggestions for effective strategies to beat each legendary as quickly as possible.
Still, it worries me that there are so many, so spread out across Tanaan Jungle, a zone that's not exactly a breeze to navigate through. There are level 100 mobs crawling all over, with some boss pets behind level 100 elites. The terrain is hilly in some parts, with crevices and other geographical traps/obstacles, so it's not really a walk in the park either.
Even with pre-determined teams to use against each boss pet, the battles do take some time, being legendary status and all. The gimmick for these encounters, Fel Corruption, also slows down the fights.
Combining travel-time with how long it takes to complete each pet battle adds up to quite a pain. I'm currently under the impression that you'll need to set aside a good chunk of time to do your round of legendary dailies each day. Either that or split up the battles throughout the day, half in the morning, half at night, or something like that.
If that's something your schedule can't manage, then the next best thing would be to park alts at specific boss pets (probably the pets you find easiest to beat) and just log on to complete those. Keep in mind that Tanaan Jungle is gated, and I don't know if sub-100 characters will be able to travel to that zone without phasing issues. So unless you have max level toons, it might not even be possible to use alts to get through at least a few dailies a day (for those with busy schedules and don't have the time).
So while I'm excited for new content and new pets, Draenor's version of BoF (supersized and fel-touched) has me wary. 15 pets to travel to, without flying, and 15 legendary/gimmicky battles to complete. It sounds like you'll need maybe a solid hour or more to get through them all, but we'll see. It will be up to each collector to determine if the four new pets are worth the (potentially large) amount of time spent traveling to and doing these new dailies.
Thankfully 3 out of the 4 Fel-Touched Pet Supply pets can be caged, but the one that stands out the most, Nightmare Bell, cannot be caged. Looks like I'll be doing the dailies until I get at least that pet. After that, it's hard to say if I'll keep up the routine for the others, or simply resort to trading/buying them.
Early testing on the PTR has me somehwat biased, leaving me with a not-so great impression of the battles so far, but I'm open to changing my mind in the future, of course.