"Metal Slug 4 (メタルスラッグ4) is a run and gun video game for the Neo-Geo console/arcade platform created by SNK. It was released in 2002 for the MVS arcade platform and is the fourth game in the Metal Slug series. 2 years later, Playmore published Metal Slug 4.
Metal Slug 4 retains the same gameplay as previous titles, with the addition of some new enemies, bosses, weapons, several new vehicles and a new bonus combo system. It was later ported to Microsoft Xbox and Sony PlayStation 2 as a separate game in Japan and Europe, and along with Metal Slug 5 as a compilation in North America.
A bonus scoring system was added that allows the player to be rewarded depending on how many enemies are killed in the time allotted. The time allotted is determined from the type of emblem that is picked up. A time meter will appear on the top of the screen, and if the player lives through the end of the level, they will be awarded bonus points for badges that represent feats accomplished. Eri and Tarma were replaced with Nadia and Trevor."
Source: Wikipedia, Metal Slug 4 , available under the CC-BY-SA License.