In my library I have all the Fallout games with the word "classic" in the title and I can see that I could buy the non-classic versions... what is the difference between them?

Oh god, not again... -_-

You didn't even bother to sacrifice half a minute to search for the answer, did you?

The "classic" versions have a couple extras missing from the new versions. The base game is the same, though.

Thanks a lot!

One other difference:

Buying any non-classic version (or any other Bethesda game on this site) will get Arena and Daggerfall added to your GOG library; the classic versions do not count for this purpose.

With that said, if you already have the classic versions and want Arena and Daggerfall in your library, why not get a game you don't already own? That way, you get a new game *and* you get those two freebies. (Alternatively, you can just download Arena and Daggerfall for free from Bethesda's website.)