Metal Slug 4
Released in 2002, Metal Slug 4 is considered by many to be the worst of the Metal Slug series. Tarma and Eri were replaced by new characters Nadia and Trevor, who were not well-received. A new scoring system and a new weapon were added, but that wasn't enough to attract fans who were hooked on the third game. Unlike the last two Metal Slugs, number 4 is mostly mass-slaughter of soldiers and tanks, making it similar to the first game in that respect.