I hate devs who think we all really need the sound. Sorry, but I still want a mute button for the voice and effects. 3/5 because of that, 4/5 otherwise.
best tower: 2 area burst towers, 1 area slow and 1 range boost.
Once you get that, you can literally call all the (non ghost) enemies at once and still win.
Doomed, you need to get the "make more swans" upgrade and the mobility ones, but not the "make more strays" one, or the increased radius. You'll find it easier then.