The first Metal Slug is weirdly grounded compared to the rest of the series since it sticks heavily with its military theme and doesn't have the weird ass occult shit future games have. The game's boss fights are pretty boring since they're mostly just big vehicles with linear patterns and the solution of just dumping grenades on them is too easy. But despite that, the game has a lot of cool set pieces and I love how much it just loves to toss huge waves of enemies at you.