Metal Slug is a timeless classic that still holds up as a truly great game

Absolutely. Y And I think it's partly thanks to its simplicity, the fact that the game is based entirely on running and shooting without thinking about anything else, makes it perfect to enjoy at almost any time, even if it's only for a few hours. For a while I had a version on my cell phone that I played from time to time for a few minutes, it always served to entertain me for a while.