I'd like to nominate Spirit of the Island as a second-class citizen game, if you please. The issue here is both with the store page presentation and the actual technical representation here on GOG. First, SOTI and its DLC Beach Resort install as a single game. No problem there, of course, but then we come to Adventureland....the supposed paid "DLC" for the base game. Its store page allows you to buy it without the base game, allows you to install it, and it actually installs as a separate game (Offline Installers). Adventureland (on GOG) is simply the base game all over again minus the Beach Resort DLC and including the new amusement park features. Obviously the Beach Resort DLC content is missing because it is installed in the base game folder. So, to fully enjoy the game, one must run the original.exe, play the game with beach Resort content, then switch to a different .exe, load the save file, then have the new content. It's a total mess and is not this way on STEAM according to other players. It is a mechanic...the amusement park stuff...not a standalone. So, here we are with a FUBAR implementation. The store page is also totally messed up for Adventureland. Take a look at the game specific forum as I don't want to write a book.
I contacted GOG support, and the Publisher, META, who has a user account here, but they don't seem to give a damn.