I wanted to show what a "prototypical" Earth Defense Force: Insect Armageddon enemy encounter design might be, and this end of level scenario and boss fight fits the bill nicely. EDF combat, like most action games, generally works best when you give the player a nice clear line of sight to the enemy's origin (that is, you want to avoid confusing the player by having unseen enemies hurt the player from many directions at once). Of course, EDF is also all about swarms and swarms of insects: so this game is also a great example of when it is appropriate to break the "rules": sometimes you actually want to swarm the player from all angles!
The trick is do have a balance between a nice, manageable combat and the white knuckled, edge of your seat adrenaline rush of getting absolutely overwhelmed. So for this encounter, I have the waves start off with manageable numbers: as you can see in the video, waves 1-3 aren't too hard, using the defensive position that the terrain (also designed by me, by the way!) provides. But by the time the spiders start arriving, I increase the numbers of the enemies as well as the "overlap" between waves, and soon you are overwhelmed: just in time for the boss, a "bomber" spider, to arrive!