I've only played Mordor but I feel they are underpowered. For the first 50 turns it feels like a 3rd rate power (H/H diff), because there is almost no infrastructure or industry. I tried "roleplaying" and building up, with trolls and everything before I set out to conquer, but because of the map size it is hard to react and defend against Gondor/Rohan. Furthermore, the economy simply cannot support enough orcs to defend the borders with.
I read some threads that advise to blitz Gondor, but this implies that I won't have the chance to replay RotK under the current balance (not without cheats)