Unreal's Kismet (http://www.unrealengine.com/features/kismet/) has been quite successful. There are a lot of little bits of scripting that go into a game where this kind of language makes perfect sense.
Make a whole game with a visual language? No thanks! Give game designers the ability to just drag stuff around when they need to tweak behaviors? Yes, please!
A note about "game designers" might be in order: a game designer can be someone with little technical experience. "Game designer" is a broad spectrum of people from almost-artists (some kinds of level design for example) through full fledged programmers (sometimes titled "Technical designers").
Make a whole game with a visual language? No thanks! Give game designers the ability to just drag stuff around when they need to tweak behaviors? Yes, please!
A note about "game designers" might be in order: a game designer can be someone with little technical experience. "Game designer" is a broad spectrum of people from almost-artists (some kinds of level design for example) through full fledged programmers (sometimes titled "Technical designers").