There are many problems with the assassins but there are 2 major ones in my opinion. 1) They get rid of half of the game. The thing that made these games great was that they were action rpg/tower defense games. When you throw an unreasonable amount of assassins at heroes, it turns into just standing in front of your towers and hoping your defenses hold up. You can't attack and you can't repair during waves because you are constantly disabled by the assassins. I've had times where every other enemy is dead including bosses, but I still have 5 assassins left. It forces people to play like they are using an afk build. This is not fun. 2) It limits the number of hero builds you can use at higher difficulties. You NEED hero health as a stat on pretty much all of your armor pieces or you die very quickly from the assassins. This means you only have one stat you can use to benefit your active hero playstyle. You can no longer use cool hybrid builds like hero damage/crit because you have to only pick one of those to use since the other spot is taken by health. Not that it matter since you are barely attacking in chaos v anyways.