Metal Slug 4 (合金弹头4) is the 2002 entry, made by Mega Enterprise and Noise Factory, which brought Nadia and Trevor in alongside the original squad.
Metal Slug 4 (合金弹头4) is the 2002 entry in SNK's run-and-gun series for the Neo Geo, and the first made after the original Nazca team had moved on.
It keeps what the series is known for — hand-drawn sprites, rescued prisoners, vehicles you climb into and out of — and adds a combat score that rewards chaining kills rather than taking cover. Two of the four playable characters are new to this entry.
Like the rest of the Neo Geo shelf here it plays in the browser from data you provide, with the key bindings listed on the page. Progress is not carried between sessions: this is the arcade build, and the arcade had no save.
All 103 games in Old Games