We ended up playing this and it's pretty nicely balanced. Both players were inexperienced (I was reffing, offering advice), and we had to quit by turn 7 at 2am, but at that point we all agreed it was still up in the air, though slightly more likely that Isengard would win. It seems unbalanced at first for Rohan, but once the Uruk-hai get into contact, the attrition rate for Rohan gets pretty steep. It didn't help that Rohan's reinforcements didn't arrive until turn 6, while Isengard's arrived a turn earlier.
The river adds a great deal of tension. Swim test required, and Isengard's player was so interested in getting across he lost a couple of uruk warriors to drowning. Berzerkers had no trouble crossing, as they do not wear armour. I also decided that the river current pulled them d3 inches per swim test, which made things more interesting.
A couple of amusing moments: one RRG killed three Uruk pikemen with throwing spears, robbing support from the front man three turns in a row; the Mordor Troll's first charge after crossing the river was on a single Wose, and the Wose turned around and drove him off with his spear.
Here's a couple pics. The rivers and the darker grey rocks are from Gale Force 9 ( http://www.gf9.com ), their Battlefield in a Box kits. I still need to flock them. The woodland bits and lighter rocks are my own creation (except the trees themselves are woodland scenics). And the WoR aren't painted...
Original deployment after Rohan's Move Phase (he moved everyone across the river):
A couple of Woses, just for fun:
