At its core, I think it's a pretty fun shooter with a nice variety in enemies, great juicy effects, a goofy story, neato bosses and so on. Reminds me a lot of games like Gunsmoke, a favorite of mine. Certainly a solid first impression and a good core!
However, while it starts out strong, it feels like it stalls out very early on: once you've gone through one level, I feel like you've pretty much seen everything the game has to offer already. You have to go through too many levels of pretty much the same set of enemies and geometry to eventually make it to a boss, which only after then mixes up the levels with the simplest of additions like someone who chucks bombs in a vain effort to distract you from the fact that yes, you are just playing the same levels still. While the game has purchasable upgrades, they felt very token and don't spice up the runs enough, with many of them feeling very lackluster and boring (like the pipe bomb, which just flashes the screen without even an animation of throwing the pipe bomb or an explosive sound effect). The game being so long also makes it much more punishing with the way it forces you to start all over on death, making me feel less inclined to replay since I don't want to retrudge through so much to get to the cool boss fights.
At the moment it just feels like a classic case of a good game being stretched thin over too much repetition and filler to inflate play time lengths. I prefer a short and sweet experience that leaves you hungry for more than a game which just keeps going until you get bored! If the game was cut shorter, for example 2 levels inbetween boss fights, or if the game had the levels feel more different by adding in more extensive variety and increasing challenge as you go on at a quicker pace than it does now, I think it would be great!