Well one key difference is all the corn based stuff they put in the US version.
Corn sweeteners have a sickly sweet, cloying quality about them, I much prefer the sugar cane and fructose based sweeteners in the UK (e.g. and IMO, Cokes taste better in the UK because of that)
Not to mention that high-fructose corn syrup is the unhealthiest of all sweeteners! It has been linked to America's troubles with obesity because it is highly caloric, but doesn't make you feel full, so you can consume a lot more of it than you would something made with sugar. Other than that, though, the ingredients look pretty much the same.
BTW, I completely agree with you about the Coke. British coke is like Mexican coke, which I used to go out of my way to get at Mexican grocery stores when I lived in California.