Sunset Riders Classic Co-op
The Matrix has 47 shooters on file for the Sega Genesis / Mega Drive, released between 1988–1997. 17 of them support multiplayer, including 8 with co-op. They're ranked below by legacy score, so the games that shaped the genre on the Genesis come first, with lesser-known picks further down.
Shooters are built around aiming and firing, from first-person corridor blasters and light-gun games to run-and-gun stages and multidirectional arcade shooters.
Typical commitment: an evening or two (roughly 1–6 hours to see it through). Tip: Retro shooters were designed for CRT TVs and original controllers; light-gun games in particular need special hardware or alternative controls on modern screens.