And sadly it's not much of a challenge. Keeping all your towers up to date with stacking all available upgrades, bonuses and boost towers will cause the enemies being vaporized before they even get to the first curve. Even the last wave.
This could be solved by multiple entry points forcing you to divide your forces strategically or create set building spots where the towers can be placed, so you are forced to consider different ranges and qualities of the towers to decide where to build what.
Viewing post in Angus Defense jam comments
We thought about requiring clicking to collect, but didn't get to it. If we took this one further, in addition to increasing the difficulty, we would probably add click to collect, and a tower that could be placed to auto-collect. We want to balance the difficulty so that you feel like you need to be placing or upgrading towers during the wave.
Thanks for all your thought on this.