I have actually only tried each one once on vet so far(didn't bother with normal). They honestly seem like they have slightly higher than mediocre difficulty. Both seem easier than vRoM and vCoS.
The problem I found is this: ZoS made the same mistake they made with vRoM, they made the mobs absolutely miserable for no reason. To add insult to injury the boss fights were disappointingly easy for such tough mobs. To me vCoS had the perfectly balanced mobs...not too miserable to fight through, but the bosses took some actual skill and didnt just depend on on DPS and a certain amount of luck(like vRoM). I would much have preferred ZoS made the bosses in the new dungeons harder and the mobs less tanky. So I rate the DLC dungeons in order from best to worst:
1. vCoS
2. vWGT
3. vRoM
4. vFH
5. vBF
6. vICP
On another note: ZoS should also have put the new motifs as a dungeon reward like they did with vCoS and vRoM...that would have added a lot of replayability to these dungeons. As it is, unlike vRoM and vCoS, I wont be pug farming these dungeons for months for motifs or much anything else. I give these new dungeons a mediocre rating of 6/10 compared to the IC dungeons 7/10, and the SoTH dungeons 8/10. I also noticed quite a bit of lag in these dungeons, which is not the case in the other DLC dungeons, but I am putting that down to ZoS bugs on newly released content.