While it does provide an idea of what kind of game it's going to be in the story, there is absolutely 0 time between the start/retry button and the beginning on the game. There needs to be some kind of pause or buffer to allow the player to see what's happening and then react to it. Otherwise, it becomes hard to figure out what's happening or why you keep dying so quickly.
I like the idea of this being based on being chased around, but I think that there are things you could implement to make it more interesting.
For example:
*There is little to no design to the layout, and it leads to it becoming repetitive extremely quickly. A small layout (similar to other games of this nature, PAC-MAN is an obvious choice) provides a way for the player to strategize beyond 'I move in a circle' and engage with the game in a more fun way.
*I think the mouse could still work, as I believe it's more dynamic than the keyboard, but you'd need to consider that dynamic movement in the design, or make 'Darkman' move in a slightly less predictable way (or, allow him to move in ways that the player cannot. Perhaps he moves by bashing into the walls when he sees the player, but otherwise just tries to move towards them).
*I'm not one to criticize for artistic ability. People have different talents and strengths. I would recommend that you instead add more details or differences to Darkman in order to make him look less like PAC-MAN, and therefore more unique to you.
I like the concept, but I believe it could be executed better with the right implements.