If ever there was a lengend of a slot online, it has to be the Thunderstruck game. This game was released online by Microgaming for the USA market originally. Then, the game moved into Las Vegas.
You don't see Thunderstruck in many casinos in Vegas, but it does exist. More likely you would find it in an off-strip casino. The fact that there are now many versions of the game tells me it is still hugely popular.