Because of balance issues the amount and strength of enemies in each wave is not random. This kind of takes away the replayability of the game once you find the solution to each mission and aquire every achievement if you ask me, I mean an endless mode was made (partly at least) because of the vast amount of requests for randomisation, so heres my idea:
Multiple sets of enemies, balanced for the level as always but appearing randomly. Example - You are at level 6, the next wave will spawn either etins, spiders or gnolls, if etins spawn itd only be 1 or 2 that appear, if spiders spawn there will be 6 and if gnolls spawn then there will be 10. That was just a rough example but basically I want the campaign and endless mode to merge together... an abomination just like the spider queen