Slave Pens - easy. just a few mobs which are unCCable, so would need to be kited. 1st boss is tank and spank with a dps watching the totems. 2nd boss, as a druid healer, prolly would have to keep the tank up, with every range trying to stay max range and you HoT them when they get aoe damage. Last boss also the same. NR for last boss makes it a bit easier
SteamVaults - a bit less easy. first boss is same as normal, 2nd boss is a balance between interrupting the healers and dpsing down the boss. warlord is cake
Underbog - between easy and medium difficulty. after the 2nd boss there are mobs which are un CCable and also the boglords which hit a truck and grow after a period of time. mini gruul ftw
Mana Tombs - first boss requires a tank with very high shadow resists or 2 healers. last boss is a dps fight. above medium difficulty
Sethekk Halls - not that hard, easier with shackle and careful of fearing mobs.
Shadow Labs - medium difficulty, have to be careful of the assassins in the inciter rooms while doing the big pulls
Ramparts - medium difficulty. just have to be aware of the pats.
Blood Furnace - medium difficulty. 2nd boss is hard, best CC for this would be fear. There are fel guards near the end boss who hit a crap ton, sorta like the boglords in UB and SV
Shattered Halls - quite hard. especially on some of the pulls before the first and 2nd boss.
Mechanar - easy badge farming, recommended
Botanica - havent done, but people said it's not that hard.
Arcatraz - heroic arc make babies cry. true story. dont do unless you have a pally or priest for shadow resist
Escape from Durnhole - first 2 bosses are not hard. make sure you have a hunter tho, since there are pats that are on fast respawns (5mins iirc) which are un CC able and they'll summon 2 adds. if you have a hunter scatter shot them to pull they wont summon the adds (changed after patch to make it easier i think). epoch hunter is still hard tho and you only get 3 tries after you release thrall.
Black Morass - damn hard, not needed for any heroic quests, just do it if you wanna test if you're keng or not

don't worry about burning your mana for the trash, short heals are the win for the crazy pulls. there's some fixes in the upcoming patch to help make heroics easier. like the cleave radius, and locks can seduce etc.