Viability: I am not quite sure where the ending of the game is supposed to be; like Josie mentioned, the white rectangles make it so you cannot progress beyond a certain point. If that is the end of the game, then the game is playable from beginning to end; if not, then I am curious to see what is beyond it.
Presentation: The controls make sense, but it would be nice to have some indication of what/where the goal is, whether it is killing enemies for points or reaching the end of a path. Speaking of killing enemies, I notice there are moments where the enemies will move above or below the player, which makes the fact that the player can only shoot left and right kind of inconvenient. I do know from experience that it can be difficult to get the player to shoot up and down, so I totally get why it is the way it is now.
Theme: The sci-fi/space theme is very clear, and I am a big fan of the design of the monsters. They kind of remind me of enemies from the Corruption area of Terraria, which I love! I am curious to see art added to the elements that do not have any yet; I want to know what the yellow triangles in particular are supposed to be. The sound design is great -- I love that you have music and sound effects already, and very fitting ones at that! My one nitpick would be to maybe turn the volume of the shooter down slightly, simply because it is a decently loud high-pitched noise, but that could just be a me thing.
Engagement: I can definitely see how things are coming together, and the game is engaging so far, but I think adding a clearer goal will go a long way toward making the game more engaging for the player.