Every few months, Humble Bundle releases a massive SNK collection where you can pay $15 for 20+ games, including every Metal Slug. You receive Steam keys (which are legit serial numbers) via email.
The "Complete" or "Collection" version for PC was a significant release because it marked the first time and Metal Slug 6 were officially available on the platform. Serial Number Metal Slug Complete Pc Download
This compilation is lightweight and runs on most older hardware: Metal Slug Complete PC Every few months, Humble Bundle releases a massive