To quote the release notes for the app, the "three-reel casino slot machine has a unique nudge feature that determines the direction of the reel once it has stopped, giving bars with an arrow a final nudge up or down." Good stuff, because sometimes once the reels have stopped spinning, you watch one or two nudge into place to give you a win.
There's an interesting back story behind this game, too. According to an article in the Chicago Tribune, Double Luck Nudge was designed by Larry DeMar, a longtime game developer who wrote the classic arcade coin-op game Defender in 1981. The to decompress from the craziness of creating an "insanely great" platform. DeMar's company has focused on real slot machine games for casinos, but he thinks that the Watch is a hot platform for the future.
As for myself, I found Double Luck Nudge to be a lot more fun that real gambling in that after the first minor investment in purchasing the app, I didn't lose any money. Highly recommended for any Apple Watch owners who want to show off a cool app to friends or have some fun in those situations where you're bored and pulling out your iPhone would be rude.