Despite the amount of work done, I am impressed you made a functional game with different weapons and an endless style round component. One improvement could be to have an enemy counter

Interesting concept with the use of elements that affect enemies differently - Having some animations/sprite work when this happens would make it obvious on which enemy is affected and how long left (perhaps having sparks that lessen over time, ice/fire that gets smaller etc.)

The choice of weapons each wave is good and could have a range of weaponry. Having "unlocked" weapons saved in a JSON and loaded on game start could give the player the option to use old weapons (and perhaps have empty slots for yet to seen weapons so players have something to work towards).

Good work from a 2-man team!

Its a very polished game with impressively fun gameplay. I like the whole loop and it could easily expand into a lot more.

The few downsides it has are: Controls seem to be intended for controller as keyboard+mouse seem VERY clunky and unresponsive. The enemies sometime spawn very close which is not the best feeling. It is unclear what values on weapons mean. 
Overall it plays very well and looks good.