To start off, no I'm not in the prt, nor have I tried these encounters. I also do know that these are currently still in the prt and changes are more than likely going to occur. No I'm not doing super amounts of research. This is more of a first look basis.
So far, with as much as the ptr testing of the boss encounters has shown I'm not impressed. The bosses are all dying, and none of them look exceptionally difficult. (Of course Ragnaros is an exception) I can't help but compare this to Ulduar, which as far as I am conserned was the glory of Wrath of the Lich King raiding. There were something like 14 bosses, some which acctually stumped progression before Yogg, even if not for long. The ptr has atleast offered, if not succeded the chance was there, to kill the bosses and learn basic strats before they modify it, a chance at all the bosses before Ragnaros. I'm sure theres one or two they havn't given a chance to test yet, but when theres a raid of, what? 6-7 bosses total and the high end guilds already have 5 of them down, theres not much left to progress come 4.2 release. It seems more of a race to Ragnaros, not progression on each boss.
Though firelands is the hype of blizzard atm, I feel, at a first look, like it's nothing exceptional. I don't hear "OMG THAT FIGHTS SO AWESOME" I'm not seeing people saying anything more then "Yeah, that fight needs more to it, to easy".
I'd like to see a raid come out where more bosses are along the lines of Sinestra in terms of, "You know it's there, you have no idea what to expect." Also the Icecrown Citadel multi unlock thing, with limited tries per lock out was a good idea.
I also know blizzard plans on releaseing new content faster, but none the less 1-2 months isn't very fast when the top end players have had the bosses on farm since before 4.2 and the last one 2-3 weeks in.