6 of the heroic flashpoints can't even be started, the last boss in the foundry one shots people starting at 30%, I found that the only two flashpoints that are completable(i.e. not bugged or horribly overtuned) are "black talon" and "the false emperor".
I did the battle for ilum with a fairly undergeared group a few nights ago.
The only thing we had to do was skip boss #2.
But yeah, generally the hardmode FPs are a substantial jump in difficulty, mostly because your group / dps have to be on the ball about maximizing DPS uptime to avoid enrage timers.