The Ent one was probably one of my biggest let-downs in BH. I really want to field a force with lots of Ents in time but with all of them being H2K except Treebeard you're going to have trouble keeping them alive much. The Winged Nazgul one boosts those monsters to VH2K within range of the WK, in addition to a few other good bonuses, and at a good price. I had hoped that the Ents would get VH2K near Treebeard or perhaps some other general bonuses. Unfortunately it only really helps if you're fighting Isengard. On the plus side, there is a nice new Fortune you can take if you have that BH that allows you to upgrade one of your Ents to VH2K, but again you have to get that BH and it's not really price effective unless you're facing Isengard.
I like the one for Thranduil's Halls. I already take at least one Formation of Sentinels anyway, and lots of WEs. It's a cheap BH for points and isn't very overpowered. You get some extra ambush options which is very well themed, and a little better Defense bonus from woodlands. If anyone wants to gripe about that tell them to bring an all D3 army next time you play.
I think the Rohan BHs are good. Reasonable costs, well themed requirements, and some good, but not over the top, bonuses. A friend plays Dwarves and the BH's he's played have been well balanced. I haven't looked much at the Gondor ones since I don't play them myself and we don't have any local players with a large Gondor WotR force at this time.
Fallen Realms has some reasonable ones I believe, and the ones for Moria and Angmar also seem pretty good. Just as their normal forces, I think the Mordor ones are perhaps the most over the top and/or undercosted. I guess there are a couple major Mordor players on the design team.