It's a brilliant shooter. There might be better STGs on the Megadrive from the point of view of gameplay, but technically I doubt there is an MD STG that can touch this. This game is sprite city with no slowdown and it features the best use EVER of mode 7 - level 2 - which consists of a huge space platform that you initially approach from a distance and then when you get up close you make several passes over it - absolutely brilliant.
I have the PAL version CIB and the JPN version cart only such is my love of this game. Loads of levels, a brilliant power up and rich weapon scheme. Lots of difficulty levels too - including an arrange mode and a suicide bullet mode. It also has a "short" mode consisting of a couple of levels for a quick score attack session. Lovely.https://www.youtube.com/watch?v=k9f5YRvydRg