Was running the instance yesterday (after searching for a group for one week) and it was really fun. Some boss mechanics reminded me of other MMOs (rotating shield buffs, duplication on death), but that is not a bad thing. I am looking forward to the next flashpoints, while being really frightened by the idea of fighting Mentor on hardmode.
Only a few things were annoying.
When we killed 2 assassins, the third ("beta") got a 100% damage absorbing shield, making him fully immune to anything (although the buff says "reduced" damage, not "immune"). The shield was reapplied every 30 seconds with a 1 second gap to hit him with one single instant spell before he went invulnerable again. I don't see any way to purge the buff or interrupt it (no cast bar). It took us 10 minutes to get him from 50% health to 0. I understand that the better way to kill these 3 is to bring them down to low health and kill them at the same time (like boarding party), but a full immunity shield in 29 of 30 seconds cannot be the intended mechanic of this boss.
Bulwark is not moving and casting slowly. When some party members die, the others can easily run out of the room. But the boss does not reset, no matter how far you run away (we did not try leaving the instance). When you get back in he immediately starts one-shotting everyone.
I don't know what to think about the green loot. There are lots of mini bosses, but I have seen better stuff dropping from trash. There is no reason for a lvl 49 instance to drop a single green lvl 47 item after figthing trash for 40 minutes. The only lvl 50 epic (lvl 52 mods) item drops from the last boss. We got an item with cunning-stats, with no IA in the party. In lower level flashpoints the loot is always usable by the group members (e.g. a run with 3 sorcs and an assassin will only drop willpower). Why does that change later on? I am not running end game group content to outfit my companions.
The Assassins are bugged in that regard, when we killed the first two the third one never had a shield flash orange or blue, and we just dropped him, although he enraged and became a hard hitting jerk.
Bulwark not resetting was quite upsetting, we hit that issue too.