Nice to be back on a real root beer with real ingredients. Sioux City is made with cane sugar and none of that high fructose corn syrup. This is another brand owned by the White Rock Products Corporation who also produce the Old Brooklyn Williamsberg root beer which I recommend (scored 8/10).
For a bit cult product placement, Sioux City's sarsaparilla gets mentioned in The Big Lebowski as seen here:
Its a good root beer and better than the mass-produced brands more commonly available in the UK (originally bought from American Soda for £1.99). If you want a no-nonsense, simple root beer then this is a good example. However, there's nothing memorable about it compared to the Old Brooklyn counter-part.
I'm being generous and rating this root beer: