Yes ..... something has definitely changed. The "solid" chocolate products, like Dairy Milk, Twirl, Flake, Buttons etc are particularly horrid. It does taste different - yes, "oily" - and the texture feels wrong. In fact, it seems to have almost no flavour at all and feels nasty in your mouth to boot.
The "less solid" (well known techical term ! not) varieties are slightly better - probably because the chocolate element is disguised by the other ingredients and flavours. So ...... Picnics, Mint Bubbly, Crunchie, Fudge etc are still just about bearable as you don't suffer that horrid cloying and flavourless gunk feel quite so badly.
And as an aside ....... though it's sort of related, IMO, Cadbury World has gone right down hill lately. I remember going years ago and being a complete chocoholic very impressed with the variety of stuff for sale in their shop - a fair proportion of which you couldn't get elsewhere. Last time I went it was just loads of "normal" stuff and very few bargains either.
I used to always get a bar of Dairy Milk for a not too expensive chocolate fix but wouldn't now. Have still got half a tin of Roses from Xmas which is unheard of - IMO they more or less all taste the same, and that's even with fruit creams and caramels included. I won't buy them again.
I don't understand why the recipe's changed - and it has, even if Cadbury are denying it. Guess when their sales figures drop far enough they might have a rethink perhaps ?