I didn't know about it until recently since it's an arcade exclusive, but it's one of Toaplan's best up to this point I think. I especially liked how they weaved the environment into the gameplay in cool new ways, like the third boss that cuts off pieces of ground with a giant laser. Each of the seven levels feels pretty unique, the action is usually fast and intense thanks in part to good smart bomb placement and the fuel mechanic (which works like in Wonder Boy), and all but one weapon are very useful. There's no weapon inventory, but you can at least avoid the worst one, the flamethrower, pretty easily. I generally stuck with the green and pink weapons, since they let you strafe. Another thing that's pretty cool is that they put cameos from three earlier games in this one, triggered based on your score I think, and a hidden escort mission featuring their mascot in the first level, with a bunch of points as a reward.

The game looks great for 1990, with careful attention to detail given to pretty much every tile. Most bosses are huge, and some have several destructible parts. As for the music, pretty much all the songs are on par with the great Hellfire and Zero Wing ost's in terms of composition while the FM synth work is solid but not quite top tier for the YM3812 chip. You'd probably think it was made at the same time as those other two just from listening to it. This was a couple of years before they started using samples in the music, and their synth drums aren't the best.

I can see why it wasn't ported at the time; top down/vertical scrolling run 'n guns weren't as popular as sidescrolling ones at that point and there's plenty of slowdown in some segments, of the kind where the game abruptly goes back and forth between slow and normal. The PS1 or Saturn could've handled it well, but I think they were bankrupt by that point.

I also was never a big fan of this kind of design where you get huge difficulty spikes for dying once later in the game. They do give you a power up or two near the checkpoints and starting with 3 bombs isn't bad (however if you had saved up to the maximum of 10, you lose 7 bombs - ouch!), but what you really need is speed, an annoyingly rare power up, and there are checkpoints right before bosses too. Perhaps playing it in 2-player helps here, though I suspect it would cause more slowdown as well. I should also mention that the game loops, and there's no ending cutscene at all in non-JP versions from what I've gathered. The second loop is frustratingly hard already in the first level (the changes in the second loop seem separate from the difficulty level that you pick in the options, with enemies shooting sooner and faster than before), so I'm content with having beaten the first.