I like the arcade-style idea of running around and gaining points from shooting the enemies. The player movement felt fairly responsive, and the aiming and hitscan felt consistent. At the moment, it's a little bare, but it feels like there's a lot that can potentially be added to it.

For improvements:

• The initial starting enemy could have been a different colour to the background to make it slightly easier to see.
• Add more types of feedback on when an enemy is hit. The cross hair did expand when I hit an enemy, but I didn't notice this until a few minutes in. In addition to this, the enemy could flash and play a sound effect on taking damage. 
• Add a mechanic that introduces variance during the game. For context, I found that the best strategy was to run in a large circle near the wall, shooting whatever was behind me, and occasionally shooting and dodging whatever was ahead of me. I would only change my pattern when fighting the large boss, after which I would return back to running in a circle. This became monotonous after a while.
  • Time-sensitive power-ups or incentives would force the player to break their own pattern to gain a small temporary bonus
  • Change the map layout after bosses or when point thresholds have been reached. Spawn or remove obstacles so that the player has to rethink their plans when trying to move around and survive.
  • Enemies having an additional effect. For example, producing temporary hazards, either as a form of "attack" or on being shot; enemies gaining a benefit after a period of time has elapsed such as strength or splitting into more. This would force the player to re-prioritise targets.

Overall, it's a game with a solid foundation to build from.

Like the game and the idea however i feel there are a few things you could to to make it alot better and accessable.

1.  have the cylinders a diffrent colour to the ground and walls to make them more visable (unless they are designed to be hard to see)
2. Make the gun play a diffrent noise when  its running low on amunition to indicate to the player a diffrent way
3. Change the UI as the ammo in the bottom right hand corner, score top right and health (?) is bottom left. It is all very hard to concentrate on when you are suppose to be concentrating on the gun and the enemys flocking to you.
4. remove health counter? I am not sure why there is a health thing in the corner as you get one hit and you died.

but still fun game to play!