Operation C Classic
The Matrix has 23 shooters on file for the Game Boy, released between 1987–2001. 7 of them support multiplayer, including 1 with co-op. They're ranked below by legacy score, so the games that shaped the genre on the Game Boy 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.