One of the most frustrating shmup I've ever played yet the one I've always loved the most. Mostly because it was the most stunning game I'd ever seen on the speccy back when I played it. And it played with a good speed, without any slowdowns, had great sound...
Some years later I discovered the Amiga version and many years after that - an arcade one.
All simply great. I know there were some "less good" ports but luckily I only played the good ones.