There's some interesting potential in restricting the player's movement like this to add something meaningful to the game in return. There needs to be more, though. Aiming is one thing, but as-is, it is way too situational. Most angles go straight off-screen from most positions.
The control scheme is awkward. Why can't I aim by holding down a key and then pressing the direction I want? Using up and down is counter-intuitive enough on its own, but the aiming uses some sort of gradual, awkward truncated scrolling for holding the keys instead of simple digital inputs on key press.
Why is the sword a toggle rather than a hold or having its own button? These state-dependent selection commands are very awkward, as I have to look to my character to know its current state. The sword felt pretty useless, too.
Why is there only one movement speed, for that matter? Movement is already limited, so by forcing me to move quickly, a lot of potential depth in that space is already lost. I can barely position my character correctly to take down the tiny enemies by lightly tapping the arrow keys.
The low base shooting rate at the start is annoying. Power-ups are a bit too high-impact for my liking.
I tried playing on hard first. I found the movement too fast for me to consistently dodge the waves on the first boss pattern, so I tried medium and had the same issue. Then I went to easy and got through the rest of the game that way. The patterns are nice, but only the swinging laser one feels like it's getting any use out of the game's 1D movement. That could probably use some telegraphing though.