Foreword: Anything related to laws will always be in a gray area, because the case outcome ultimately comes from a handful of people.
Others have accurately pointed out that game code and assets fall under copyright law and that product, company, etc. names fall under trademark law.
However, although others have pointed out that you cannot copyright game mechanics, this isn't 100% true.
Let's look at the legal history of Tetris, a game often cloned by new game developers.
In mid-2006, and in late 1997, TTC's legal counsel sent cease and desist letters to Web sites on the basis of Tetris-type games infringing the "Tetris" trademark, trade dress, and/or "look and feel" copyright. Around 2009, TTC and Tetris Holding LLC brought legal action against BioSocia, Inc., on the grounds that BioSocia's "Blockles" game infringed on proprietary rights that were held by TTC and Tetris Holding LLC. On September 10, 2009, the legal case against BioSocia was resolved, with BioSocia agreeing to discontinue making the "Blockles" game available to the public. In May 2010, TTC's legal counsel sent cease and desist letters to Google insisting that 35 Tetris clones be removed from the Android Market. A US District Court judge ruled in June 2012 that the Tetris clone "Mino" from Xio Interactive infringed on the Tetris Company's copyrights by replicating such elements as the playfield dimensions and the shapes of the blocks.
Tetris and Mino
So are game mechanics copyrighted? The answer, as with many legal issues, is maybe.
Read more about Mino vs Tetris here.