Aza\Caly, i think it will be a great improvement to add some "randomness" to the waves, allowing a random choice between multiple themes for a single wave, with different bosses.
I will give you a simple example to clarify what i mean:
Suppose to have:
- 2 waves;
- 5 themes (i don't know how many you have), Doom, Quake, Unreal, Dino, Tony;
- 1 boss for each theme.
FIRST WAVE:
- random choice between Doom and Unreal;
SECOND WAVE:
- random choice between Quake and Tony;
It can be useful to have also multiple Doom, Quake, Unreal and Tony waves (please, remember i don't know all the types and all the monsters), so that the monsters spawned are different basing on the wave (with pupae there are some easy bosses, with nali elder there are other monsters, with the blue gravity nalis other monsters...).
For example in one wave of tony there are some monsters (jakob and so on) with a boss (tony boss, the dancing reaper) and in the other wave different monsters (or different number of them) and a different final boss (tony dragon?).
I really think this will be great

Thoughts?
EDIT: also, why not a skill-score like on freon to measure the points made in the last matches without significantly high\low values? (not the most important i know)