Bullet Bros is the kind of co-op shooter where the chaos is the point. Two players tear through side-scrolling levels armed with whatever the game hands them, working out a rough division of labor on the fly — one covers the left flank, one covers the right, or you both charge headfirst into the same cluster of enemies and sort out the friendly fire accusations afterward. It's short-session gaming at its best: easy to start, hard to stop.
Player 1 uses the left side of the keyboard; Player 2 mirrors from the right. Each level sends enemies in learnable patterns, so the first run is chaos and the second is strategy. Health pickups are scattered through levels — calling dibs on them is at least half of the game's social contract. Rounds are quick enough that losing doesn't sting for long.
The shared-screen format forces real-time communication that most multiplayer games outsource to a chat window. You can't mute your partner or blame lag when you're sitting next to each other. That constraint turns a simple run-and-gun into something more memorable.