Metal Slug Warfare is a shoot'em up that is being developed by Studio Vetea. This video shows a demo version of the game.

You can find the demo on

https://vetea.itch.io/metal-slug-warfare-demo-megadrive

The game is a fan-game based on the Metal Slug series. It takes assets from the games for most of its graphics. The game is more simple than the original series. You get dropped into a horizontal level and need to survive as long as possible in order to get a high score. An endless amount fo soldiers will appear, as well as helicopters. If you shoot down a helicopter, it will take some time for another to appear. P.O.W.s appear in the level, and an arrow will show you in which direction the next P.O.W. is. Freeing one will give you an item, like a stronger weapon, grenades or health. Unlike normal Metal Slug games, you have a health bar. Scoring enough points will increase your rank. Once you reach a certain rank, you unlock another level.