i got around to play this and eeeeeehhhhh i feel disappointed
it's not a matter of this game not being cave story or not being a metroidvania,it's just that while the music and retro pixel art is still top notch, the rest of the game is not that much fun to play... the reason is because kero blaster feels a lot more sluggish than cave story, the way the game control is that as long as you hold the shooting button you keep shooting in that direction so it's possible to keep shooting right while walking backward to the left, but that also means that if one enemy is attacking you from the above and another from the side you have to shoot the enemy on the side,release the button, press up and then keep pressing the shooting button and it feels awfull, why can't i just press up and shoot in all the direction i want?
most enemy are stationary and shoots you from afar or just bum-rush you so the end result is that you spend most of the game picking enemies sloooooooooowly from a safe spot rather than actualy dodging attack since as soon as something come's at you, you can just run away back to your safety zone while still hitting the enemy,this is made worse by the fact that you are quite frail and actualy die in 2 hits (although you can buy health power up... i ended the game with a max of 5 hearts i think) and i can't help but think that the reason the game play this way is because if they made it a faster-paced action game it would have been hard to play on mobile phone's
similiary the weapon you get are all quite gimmick, there is a laser gun, a wide shoot, a bubble blower that make bouncing bullets and a flamethrower, you get the bubble blower upon ending stage 2 and ehy coincidentaly stage 3 is full of enemies that are placed in a way that they can only be hit by bouncing bullets! right after you get the flame thrower, the game throw you in an ice stage where most enemies are weak to the flamethrower and it feels super forced like if they gave me a mouth gun and sent me to candy land! Later in the game you also get a jetpack, remember how fun it was to zip all around with the jetpack in cave story? there is a jetpack in this game too but in this game it just let you do a weak double jump that is barely needed...
the bosses are fun, they are varied, colorfull and require you to pay attention and dodge shit properly rather than just hide but honestly it feels like every stage is just a chore you have to do before they'll let you eat the cake and as a result the whole game suffers from it
there are some story element that i tought were done decently but they never go anywhere...
spoiler (click to show/hide)
like cave story there is some sort of obscure force (this time represented by dark blobs) that is some vague represention of mental trauma, these blob have taken hold of the cat president the frog you control work for and of several teleporter scattered around the world and it's the job of the frog of getting rid of them by shooting the shit out of them

i found the idea of a cat president with sunglasses, an angry demeanor and a troubled past kinda funny but the game never tells you what about her past is so troubling in the first place which is disappointing
the game is also really short, more short than i could ever think, in fact i finished at 1 hour and 40 minutes mark, and i'm pretty sure i could have done it even quicker if i never died... after finishing the game
spoiler (click to show/hide)
there is a new game+ mode where the frog get recolored gold and all your health power up get taken away leaving you with only 1 HP (but you can rebuy them back so what's the point?) and you keep all of your weapon upgrade's,there is a new weapon to use and finishing the game twice unlock a boss rush,honestly it all feels like pointless addiction
here's a review which i think explains this game problem better (although in a somewhat pompous sounding way)
http://killscreendaily.com/articles/kero-blaster-world-search-game/