Dragon Unit was released in 1989 by the little-known Athena co., and it's an odd kind of hybrid platformer/beat em up. Odd because rather than being a platformer with beat em up elements, there are instead two kinds of stages: straight platformer stages and other stages that are mainly a long, flat corridor of enemies, but have two Guardian Heroes-esque planes to switch between by pushing the joystick up or down.
Other than that, and the fact that the shield the protagonist is carrying actually does block small projectiles, it's pretty unremarkable, mechanically speaking. There's lots of enemies, a whole range of power-ups and different weapons to collect and all the typical stuff you'd expect from a 1989 arcade platformer. Its charm lies in its presentation. At the most basic level, you can plainly see that the sprites are big, the colours are bright and lurid, and it looks pretty nice, though the black outlines on everything are a little ugly. Looking further than that, there's nice little touches, like how your knight's armour gradually falls apart as your health decreases until he's in his underwear, like a more gradual version of Arthur from Ghouls and Ghosts.
There's also a lot of visual variety in Dragon Unit. Even though there are only six fairly short stages, they all look completely different to each other, and mostly have their own sets of enemies, who are mostly big and always ugly and evil-looking, which is nice too. It's a game that mostly gets by on its atmosphere, the ugliness of the enemies, the overly saturated colours, and so on really make it stand out. At the same time, it's all very rough around the edges, I don't know whether it's down to a lack of experience on the part of the developers, or maybe budget or time contraints, but the whole thing looks, sounds and feels very unpolished.
That's not necessarily a bad thing, though, and I'd say it actually adds to the game's appeal. It could have given the impression of a game lazily knocked out to fill a quota, but instead it feels more like a labour of love, made by a team whose passion and creativity slightly outweighed their technical abilities. I'd say it's definitely worth a look and a credit feed through at the very least. There's apparently also a NES port, called Castle of Dragon. I haven't played it, but I can't imagine it being a game that makes the transition to such an underpowered console gracefully.