For me it's an on-/off relationship over the years.

I usually am fine with the Diet Coke at McDonald's in Germany (it's cold), but not a fan of the stuff I buy in plastic bottles. I do like Diet Pepsi but not Max (I find it tastes very artificial). Coke Zero is so-so.

And the weirdest thing is that we have Fanta Tangerine, which they switched from sugar to only-as-diet a while ago and now I can't drink it because it tastes so horrible.

TLDR: Either my sense of taste is just broken or they're actually switching the recipes every few years. Or it is actually this phenomenon here.