Well, I don't know about it being a "Mighty" Bombjack (doesn't state it on the title screen and there's no Mighty Bomb Jack on Mame), but it is definitely different. Bomb Jack arcade was a vertical screened game, and the ST version is a horizontal, which means the two are quite different. Whether the ST's is any better or worse than any other computer versions I couldn't say - it's the only version I've checked out, but it isn't bad; admittedly not as good as the arcade, and naturally not as good as Bombjack Twin.