The 338 Ultra is very accurate, flat shooting, and hard hitting.
It takes an experienced and determined shooter to master this beast, but I think that in the right hands it is one of the best long range cartridges ever conceived.
Despite what others may say I find the Ultra hits with significantly more authority than the 338 Win. An animal hit with the 338 Win usually bounces 20 yards and then tips over while Ultra shot game often reacts like it has been hit by lightning.
I also find the Ultra overall to be less fussy and more accurate than the 338 Win.
Weak bullets are a mistake in this one.
Though the recoil is significant it pales compared to a 416 Rem of the same design and weight (I own both).
Unless you intend to shoot game beyond 300 yards I think there are easier rounds to shoot that will accomplish the same result in close.
Remington builds the 338 Ultra's too light. Adding a 1/2 pound or more of weight goes a long way to taming the recoil.
Most will find the factory Remington's recoil more than they are comfortable with. Plan on (at least) modifying the stock to calm the beast.
Depending on the hunt I run either Leupold's 3.5-10x40 or 4.5-14x50 Lr.