I like the idea for the game but I found it to be very easy. On the later waves it's actually quite difficult to lose intentionally. I think the humans should die quicker and be able to overlap so that they die more quickly. As it is currently, it takes a very long time to kill more than a few of them. I also think it would be nice if you could pick up the currency around the map so that there was a bit more to do without the abilities. If you decide to continue developing the game it would also be nice to procedurally generate the map. It would give a lot more variety to each run.
I really like that there is an actual online scoreboard. I think it would be fun to see that at the end of each run.