I liked the cohesion of all your asset packs. Good choices.
I would have scaled the drones up a little to make them easier to hit from further off and maybe added more blocking elements to the environment; maybe made a line of trees that the drones can't get through so that where I'm standing really makes a difference. Multiple spawn points and points of entry that have blocked line of sight from one another so that you have to make a decision about where is best to stand would have been good.
As a stretch goal, I'd have made the chickens run away from the player if they get too close so that they can be herded around the map for another strategic choice.
Finally, if the asset packs allow it, I'd add some verticality, making it possible to get a good view over what's happening in certain areas but sacrifice the ability to get up close and personal with the drones/ lose the ability to change position easily as the next wave comes in.