'Nearly unstoppable' is the key here. A new player may find it impossible to stop, but every culture can counter it with a bit of foresight and practice. Hersir all fall quite quickly to arrow fire, so....
Greeks: Toxotes & both Heroes
Egypt: Pharoah/Priests & Slingers and/or Axemen
Norse: Throwing Axemen with a few of your own Hersir.
Atlanteans: Hero Turmas & Cheiroballistae
...and try to keep your ranged units behind some sort of protection (infantry, forests, buildings or walls) wherever possible.
Keep Myth Units out of the way unless you see an opportunity to safely move them in against the enemy Myth Units.
Try to get tower upgrades ASAP (moot point for the Egyptians).
Worth bearing that lot in mind when you try the Loki Hersir rush against an experienced player, although Atlanteans and other Norse can have headaches with it, so it's always worth using against them...particularly Gaia.
Cheers
[This message has been edited by Centaurus (edited 02-08-2005 @ 06:25 PM).]