Great job for a first game, The level design was really good and the game had nice graphics. I would have loved more levels.
You should try to add some music and sound to your game, it makes an incredible difference. If you want you can check out BFXR, Its a free sound generator.
I dont know why, but the game had a problem with the resolution in UnityWebGL (I had to go fullscreen to be able to see the game correctly). I ve never used UnityWebGL, so I cant help with that yet. My advice would be adding a downloadable version of your game. I heard that a lot of people had problems with UnityWebGL and tend to recommend playing the downloadable version instead of the web version for a better user experience.
on level 3 you can just AirStrife behind the wall. I didnt have to use the box.
Overall the game was really fun :D