I just randomly came across this one, so I had no clue what to expect going in. Never heard anyone talk about it, never saw any images of it before, so from my perspective, it seems like a show that was largely lost to time. But thanks to the strange world that exists on the internet, these things sometimes resurface.
Dragon's Heaven is a very simple story. There was a war ages ago, not too many details are given, and a robot with artificial intelligence is unable to return to his ship after the battle and instead shuts himself down until he finally detects human life once again. He wakes up and teams up with a female mechanic as his new pilot to fight an old nemesis that seems to still be alive and is harassing the humans alive on the planet. The actual plot doesn't get any deeper than that, it is that simple.
Were I to just judge this movie purely on its plot, it's largely dull and barely anything happens. You could fit all of this into a twenty-minute TV episode and nothing would be lost, but it's a forty-minute OVA. Considering all of the focus is pretty much on Shaian (The robot) and Ikkuru (The new pilot), the entire narrative interest of the show rests on those two's chemistry. Thankfully the two of them make a really fun team. Their dialogue is often funny, they are both very charming as characters, and despite how little time they have together the show does a great job at making them feel like a cohesive unit.
That said, on its own that isn't enough to sit through the movie but to help make it better is the actual action and art style. This show has a certain old-school grit you don't often see in anime anymore, and it captures the feel of a dark and dirty world on the edge of apocalypse under the Brazilian Empire (I don't know why, but Brazil is the evil empire amuses me greatly). Some things bother me, like how Shaian seems an entirely different sized depending on the scene, but overall the show does look great.
As I said there, there isn't much to discuss here. But it's a good OVA to watch for how short it is. It tells its story well enough, you have some great chemistry between the two to enjoy, and some pretty enjoyable fight scenes. It may not be an all-time classic, but I'm glad that this show has managed to resurface. Give it a watch if you can.