When I hit play, the screen turns black then nothing happens, even though there's an anno4web executable running when I check task manager.

EDIT: The game seems to run when I use More -> Other -> Anno 1404 Venice. I don't know what I'm missing here.

Sometimes the Anno4Web.exe and the Anno1404.exe remain running after you close the game. You have to shut them down manually with the task-manager in order to start the game again.

That said, it's pretty confusing from an UI point of view, that you start the basegame without add-on when you click the "play" button. It is the "Gold Edition", so one would assume that you don't need to navigate through a couple of submenus to start the actual game with add-on...

I think this is also the problem of some people claiming in the user-reviews, that there is no multiplayer at all. Multiplayer was introduced with the add-on. They simply start the wrong game, because the galaxy-client starts the basegame by default.

This is something GOG really should consider changing, since it seems the game is still pretty popular these days.