You've done a good job recreating the aesthetic of the famicase.

Quick thoughts

• Scoring system would add replay value.
• May want to delay spawning enemies or spawn them further away from player. It's frustrating to take damage immediately after starting.
• I found the controls very hard to handle, it feels like an odd mix of TPS and 6DoF. Have you considered removing gravity and just making the player control like a ship in a 6DoF game?
• Crosshair does not reflect actual fire direction which made aiming at enemies very difficult. If you want to keep current 3rd person perspective then one possible fix could be to raycast from camera and angle gun to face where raycast hits. Alternatively a laser sight could help.
• It felt a bit unbalanced, but honestly it might just be I was bad at it.
  • Maybe slow the speed of enemy projectiles to make it easier to dodge them.
    
  • If you do rebalance things, you may need to nerf slomo, for example have a recharging meter for it.
• Visuals and flashing effects are a bit hard on the eyes. It'd be great if you could tone it down a little
  • This also applies to the game page, maybe add a warning about it and replace the gif with a Youtube video (so it doesn't auto-play)
• Power-ups and alternate weapons would make things more varied.
  • Power-up that grants temporary invulnerability and makes it so you kill enemies on touch. Which would be an interesting reversal to fleeing from enemies all the time
  • Railgun with hit-scan projectile that penetrates enemies but has slower fire rate.

• Really should add option to change mouse sensitivity.
  
• At certain camera angles the coffin blocks the view.
• Sometimes the muzzle flash did not disappear.