Nice idea. Kael, hope you will like it. Sorry that i post it here. I didn't manage to find sticky thread with suggestions.
First it was very difficult for me to play FFH2. But after a month when i developed new strategies it started to be very easy. Even in a Prince difficulty with 5 rival AI teams with 2 AI civilizations in each team. Even Acheron is not a problem. Normally I subdual him on 220-250 turn after animal mastery with Alazkan The Assassin. By the turn 300 I conquer entire world, conquer all 10 rival AI. Armaggedon also is not scaring any more. I rise armageddon counter via "Last Days" option and razing rival cities for purpuse just to be able to steel equipment from Avatars to enhance my Alazkan.
(Putting Deity difficulty to make the game more interesting is not a solution because AI will just produce hundreds of units)
Evil environment appears not so dangerous and not so evil. I propose to include one optional possibility into the game. The Black Tower. barbarian extremely evil and powerful city. It can have some nice art like Sauron's tower from Lord of The Rings, the huge slim elegant black tower. The idea is that approximately by the turn 250 barbarians create The Black Tower which is pure evil and dangerous place. It has powerfull guardians, much more powerful then Acheron, and this place spawns extremely powerful creatures and holds rare artifacts and treasures inside them and a tower itself. I Think It can spawns liches, manticoras, ogres, wraith, mistforms, beasts of Agares and even may be mighty moving death dragons (strength 18+). (all beautiful made arts which were not included into the game can be included here like unique spawning hostile barbarian heroes and creatures). Terrain around is unfertile rotting undead desolation. To conquer the Black Tower should be really challenging, this is so difficult that it can be even the optional victory to the player who manage to do this. In most games The Black Tower simply will destroy every single civilization on a continent.
The main idea is to feel again the immensely desperate situation of persisting in evil Erebus world. The Black Tower should be more powerful then a half the rival AI altogether. To conquer The Black Tower is unachievable act of bravery. This is a task for the player who already conquered the half of the known world.