First glass I had, I went, uh, I think this has gone bad? My host said no, tasted normal... but since I was rather used to drinking milk a lot, we tried a few different kinds (less fat, more fat, whatever) and brands, with invariably the same result of it tasting completely off. It took me quite a while before I figured out that it's the pasteurization process that is completely different and leaves a very different taste. So I just gave up on trying to drink milk when in Northern America, except with cereals when there's something making it taste less bad.

Of course, when Clover/Lupine was here a while back, and she drank our milk, she thought it tasted really bad as well, so I suppose it's all a matter of what you're used to.

To get more technical, American milk is generally pasteurized with a process called HTST, which results in it having a certain taste and requiring constant refrigeration (I thought at first that was just another example of that American obsession with eating/drinking everything either really hot or ice cold, but turns out there's actually a good reason for it this time). European milk uses a different process called UHT, which results in a different taste - more pleasant if you ask me, but there's no accounting for tastes - and milk that does not need to be refrigerated; keeping it in a cool storage place (for months if need be) and just refrigerating it shortly before use works fine, and even that is not actually necessary, it's just nicer.