I know, I will get a lot of down votes from the fans but I dont care. :)
This game has very beautiful and interesting retro graph. I loved it. The only reason I went through the whole game was to see the most of it. The sounds and the music are good too.
But as a game this is a terrible one. Really.
Originally this game was an arcade game. It was designed to stuff coins. It is impossible (!) to play it through without a lot of continues, no matter how good you are. Im not an experienced 2d shooter player, so there must be ppl who can make it with half of the continues than me, but Im sure its impossible to play it without them. That is understandable for an arcade game where the profit comes from the coins ppl have to throw into the machine, but its a very bad experience on other platforms like PC.
You have 2 choices: play it wiht limited continues and you wont be able to go too far, or play it with unlimited lives but thats not a challenge anymore, just an interactive action cartoon (but a very nicely drawn one).
The controls are terrible - cant aim and move separately, cant aim in angles. "Impossible to dodge boss fights" - and they are ridiculously long and boring. Spawn - drop all the grenades - shot five seconds the same spot - die without a chance. Repeat this at least for 10 minutes at every boss...
Im sure it was a great coin harvester arcade machine but on other platforms its simply a bad mechanism.
If you really like the art style perhaps buy it on a sale and you can play it as an interactive action cartoon for 1,5 hours and thats it.