Vanguard is a horizontal shoote–
Oh wait, it’s a vertical shooter, too. Vanguard is a horizontal and vertical sho–
Wait, there are the Rainbow Zones. Crap.
Ahem. Vanguard is a shooter that has multiple stages, some of which are horizontal, a couple vertically, and a few actually go diagonally. Either way, you use your ship that can fire in any of four directions (using buttons dedicated for each fire direction) to fend off the enemy ships while avoiding their fire and other obstacles, including the levels themselves. It’s a really fun and memorable shooter with good music, including the intro music which many recognize as the Star Trek: The Next Generation theme song.
Unfortunately, the emulation in mame has some audio issues, including your ship’s lasers and a lingering noise from the force field on one of the levels. Not a huge deal but can be annoying. Otherwise, the gameplay works just fine as long as you have a gamepad or control method that can simulate the four-direction firing method (cross button gamepads like the Playstation pads work just fine).