Not impossible to complete. The firing rate is slow, but not unmanagably so. Biggest problem is that the guns just refuse to fire unless you're aiming directly at a creature. But that can be overcome with, well, practice.
We successfully completed the FP last night. First encounter admittedly took almost a dozen wipes till we had memorised every single spawn point, but we got it down. Got some good loot for it, too.
Subsequent encounter was interesting.
Final boss was quite fun and relatively challenging, too.
The fact that it seems every other attempt someone had an issue getting onto the turret to begin with was a huge headache (Ive had it where you "mount" the turret, but cant control it. I've had to click it 1-3 more times before I actually control it). That almost guaranteed a wipe.
Combine that with the fact that the shooting speed is highly unreliable and many of the ranged cociloids spawn already shooting at you and you have a recipe for disaster. The group I run with has never wiped to any boss (even the first time we ran into the Republic Boarding Party in MR) and we struggled for about 1/2 a dozen attempts before we just gave up and went back to questing.
Extremely aggravating and not enjoyable whatsoever aside from the first attempt when it still had a novelty feel to it.