I would give Isgenard a 4. The Hero selection is limited, but I think that is appropriate given both the book and film treatments of Isengard forces. I do so much wish that more players used Wildmen and Orcs more in their Isengard armies as I never got the impression from reading that the Uruk Hai were the mainstay of Saruman's force, but since many players use PJ's films as primary inspiration it is what it is. With some variety of troops it can be just as strong but even more flexible and visually appealing.
Lurtz's Assassin Shot is a great threat to many Epic Heroes and with his other dueling abilities makes him a good combat leader. Saruman (like any Wizard) is a matter of taste and play style below about 750 points, but I think he is very well suited at that level or above. You need to obviously protect him (again, like any Wizard) from enemy Hero-hunting, but if you do then you should find his spells can mean a world of difference in how the battle unfolds.
The sappers are cool models but very risky. I love to try to trigger a boom as they are being rushed past the main formations.
Doesn't happen often, but when it works it's a thing of beauty (but not to the Uruk player!). I haven't had sappers reach my force yet so I can't tell you how bad they hurt so they may just not be worth it. Maybe if facing a player dug into defensible terrain they are more appropriate.
You have a couple options for ranged attacks in the army, which is nice. The Uruk Crossbows are fantastic, but (like Berserkers) are expensive to field in large numbers. Isengard was my first SBG army and though I thought I had a decent number of Crossbows for even a 750+ point SBG force, I barely get past one Company in WotR. I'm holding off for plastic XBows. The Siege Crossbow is a great looking model and pretty dangerous vs. large Formations, especially if you can get two on the table in larger games. And of course you can pack in several Companies of cheap Orc bowmen as a nice harassment Formation.
Berserkers are a key shock troop. A couple 1-Company Formations of these can zip quickly and easily around larger Formations and do some brutal damage on Flank attacks. And they look good doing it!
I think these are one of the best things about Isengard armies, though you need to be willing to suck up the cost to get enough (but that really goes with almost any army since they all seem to have at least one metal-only Formation to spend a couple hundred dollars on).
I think the most common, and effective, deployment of a pure Uruk force I've seen personally has been one large block of Uruks with shields, with two flanking blocks of Pikes (each about 1/2 size of the main block) and a couple 1-Company Formations of Berserkers scattered in there. But that should be the beginning.
Warg Riders are an excellent way of really beefing up an Isengard army. They are a pretty effective cavalry in WotR (sorry I didn't have time to get involved in the discussion them earlier), especially if you give them a Captain to At the Double. Treat them as expendable scout forces to engage weak edges of an enemy or slow them down / distract them. Two Formations, each of 4-6 Companies, would be my recommendation. Not very much money or points to get on the table but really helpful.
I think an Isengard force could also really benefit from a couple Formations of expendable Orc troops for similar reasons ( slow/distract an enemy Formation or provide a buffer around your flanks). Many Evil players should have enough Orc sitting around to put together a reasonable Formation or two without much challenge.