This game was one of the hardest I've had to work on, not because the sound design was super challenging, but because the game itself is so very fun and rewarding. On more than a few occasions I'd start to test or mix an asset by playing, and then 10 minutes later forget that I'd intended to test, not play!
This was one of the first games I'd done a complex event / blend + random container set-up (Using AudioKinetic's Wwise). Each of the new waves and level completions can trigger an event that randomizes between a multitude of different wave "headers" (the line of dialog that denotes what type of wave is incoming) and a second set of assets for "flavor" (a line that comes after the header, giving more insight to the wave or jabbing at the players). All of this was achieved with a single event per wave type. It made life on the programmers much easier.
Speaking of the announcer, that aspect of the game almost didn't make it in. It came down to a decision between working an extra 30 hours on my own time to make the game that much better, or... Yeah no, I can't think of anything I'd actually rather be doing than making an already awesome game MORE AWESOME! A majority of the lines were recorded, edited processed and implemented into the Wwise project (and subsequently, the game) days before Gold.
One last system I was particularly fond of: Berserk Mode. With a single event and RTPC (Real Time Parameter Control) and switch call, we were able to have the music duck, filter all enemy sound effects, add additional sounds to enemy deaths, introduce a heartbeat and dynamically increase/decrease the effect of all of these based on how many enemies the player killed during the duration of berserk mode. This was all done to further drive home the gameplay effect that happens during this time frame. For every 2 enemies killed the player would move faster, do more damage, shoot faster and regenerate more health. Since the gameplay aspect of the mode scaled as the player did better it only made sense for the audio to follow suit.