Read the title
I've been contemplating purchasing this game under the assumption one can play with a keyboard alone, but I wanted to make sure by simply asking.
Is this game worth buying? Generally speaking also.

No, a mouse is not required to play. The game has full support for playing with a keyboard, and with a keyboard.
I went to the steam forum and the developer had made a pinned post describing this.

"Aim mode is impractical to use without a controller.
This feature was designed for a dual analog controller, as the game was generally designed to be played. That said, full keyboard play is possible, with keyboard rebinds available in the menu. However, the particular feature of aim mode is not really effective on a keyboard at this time. In the future I'll be looking at ways to retool it to be more usable on a keyboard/mouse. For now, just know that aim mode is not really required to progress, and it's quite possible to play the game without using it."