Black Tiger is a really neat 1987 title from Capcom that was one of the first arcade games to incorporate elements from console games -- things like branching non-linear paths through some levels, upgrading your weapon and armor, and hunting down money in the levels to buy said upgrades and items.
The game is the origin of early elements that would go on to be better developed in Magic Sword
and the two Dungeons & Dragons beat-em-ups
a few years later -- things like freeing prisoners and entering shops en route, having to collect keys to open treasure chests, combining a strong melee weapon with simultaneous release of weaker projectiles, status effects, etc. The Ghosts and Goblins team developed this one, and you can see how some of the enemy design and gameplay elements carry over here too, most notably your armor gradually crumbling as you take hits until you're running around in your medieval boxers.
The big difference here that wasn't expanded on in later spiritual follow-ups is that levels tend to scroll vertically as much as horizontally and have a bunch of little nooks and crannies to find hidden stuff in. One main feature of the levels are optional "dungeon" rooms, which are basically little mini-levels that are packed with treasures, but also with dangers. Die in a dungeon room and you're kicked back out and it is sealed off to you for the rest of that playthrough.
Though it's an interesting game and very solid mechanically, the one big thing that really sets it back is being too reliant on cheap hits for challenge. There's just way too much stuff that falls on you or jumps out of the floor with no warning whatsoever -- you just have to get killed by it and remember that it's there the next time. A common technique of the '80s to suck a steady stream of quarters out of your pocket, and one that does not hold up well today at all.