This shows some good promise, especially with its initial first impression, but unfortunately the gameplay wore thin for me rather quickly and left me feeling rather let-down. Feels like a case where the game's meagre content has been stretched out to artificially increase playtime, making it paced awkwardly, going on for too long and becoming repetitive.
As said, it all seemed pretty good at the beginning. Pretty cool intro scene that reminded me of Contra 3, a very nice controls menu where you can both see the controls and preview them in a little simulation box. Moving onto the gameplay, there's some decent classic shooting action with all sorts of power-ups and upgrades, and new enemies being introduced to spice things up, alongside bosses, as you press on. Not too shabby at first glance!
However, as said, the game just feels incredibly repetitive and boring as I got into it. Levels just feel endless due to a) the enemies showing up randomly instead of in interesting formations or waves and b) there are no interesting obstacles or events to contend with, like maybe blocks/walls you have to shoot through or mountains to weave out of the way of.
Furthermore, it doesn't really feel exciting to shoot enemies as they feel a bit too spongy and don't provide satisfying damage/kill feedback, and power-ups feel awkward in that it just feels random in what you get instead of being controllable in some way, such as Twinbee's bell juggling system.
In summary, it feels like way more exciting events happen in the first level of Galaga than this game does over its entire playtime. In this, you just hold down the trigger and try not to fall asleep.
I feel like the first step to helping this game would be to condense it down: for example, I feel like the first level would be much better paced if you would compress all four sections of the first level into just the first section, that way all of the new enemies would be introduced at a good pace and it'd end with the boss fight in good time before it gets too repetitive. But more so than that, I feel like this game needs more craftsmanship to its levels to give them a story, a flow, a rhythm to it, with all sorts of waves and formations and events and such, instead of just a load of trash you shoot at for way too long. Look at other shmups and see how their levels are elegantly constructed.