We have done Taral V, Battle for Ilum, The False Emperor and The Esseles on hardmode. Sure we wiped like 7 times on the hardest bosses, which often seem to be the 2nd or 3rd. But most others were 2 or 1 shot. We also had problems with loot chests being locked after killing a boss, or getting the normal mode loot table, but we found the flashpoints themselves to be easier then expected.
You managed to get past the Gark ? (the guy who spawns waves of adds) What strategy did you use ? We managed to get him to 20% and enrage with 1,5 healers, but with a lone healer someone would always die during or right after the stuns.