QFE -- Most tetris clones have been shut down simply by the threat of a lawsuit, even though the Tetris company would likely lose in court, because the 'clone' developer hasn't had the money to hire a lawyer to defend themselves.
For what it's worth, you're always at risk of being sued.
Trademarks cover names, so if I make "Hodgman's Risk", then I'm infringing on the "Risk" trademark.
Copyright covers "creative works", which usually just means art/sounds. In that tetris ruling, they also covered what basically amounts to the User-Interface layout as a creative work, and that's what sunk the defendant -- they copied they way in which the (unprotected) mechanics were conveyed to the player via the UI.
IMHO, that's a very grey ruling as it arguably violates the precedent of Scènes à faire (i.e. it's hard to express the rules of tertis without using that kind of UI layout), and different laywers/judges could've resulted in a different ruling.