Art's great, plays fine, the music is good too, I don't get input lag like some people do, but it's got shit Arcade design and it should allow you to remap controls. Every game in this day and age should to be honest.
That said, the grenade enemy mountain, followed by a tank protected by smaller enemies peppering you with projectiles constantly, the platforming you have to do later on through grenades. Whatever porn content this has isn't worth coin-munching bad design, on the first level, for a demo. If they decide to fix that it'll be pretty cool. I like the aesthetic a lot but they lost the script on level design and they don't know what difficulty is, it's meant to be challenging not abjectly unfair, the limited movement and attack options don't balance out the amount of projectiles on-screen and how your only options get destroyed by the far more numerous enemy projectiles. The fact that if you die you have to restart makes it even worse. In Contra you could tank a death and move out of an unfair scenario but in this you get plopped back at the beginning. That's bad and there's no checkpoints.
I used to speedrun Contra, that game series was hard as balls but when you died you got right back up and kept going, and even the infamous waterfall level wasn't this purposely cheaply unfair. Going back to the start of the level after taking a death to something so cheap? Eh.. I don't know why Indie devs are like this sometimes.