Halo is one of the most influential game franchises of all time. Ever since Combat Evolved in 2001, the series has changed first-person shooters and online multiplayer forever. While fans don't get their hands on a new Halo title every year, there has been a significant number of entries in the series by this point. They've not all been classics, though. Some of them will rightly be remembered by gamers for eternity, whereas others are just mediocre titles that even die-hard fans will forget.