Didn't get the beta this week (UGH!), but I watched a game last night where upper-level heroes were getting whacked by any number of things. Everyone in the chat was agreeing that it really is a much more dangerous world.
As far as WoM goes, I only make units to defend my cities. I tpically take *one* champion, buff him up with intelligence and spells, and annhilate every other faction and their cities (playing on hard--150%). All you would have to do is learn the fire and water tree, get intelligence high enough to cast spell immunity, firestorm and blizzard, buy some legendary armor, sword of vengeance and all the amulets and rings, a fast mount (spider, etc., that can make 4 or 5 moves/turn) and you can knock out a city with 900 defense rating with that *single* character and not take a hit. To me, that was way out of balance. A master mage, first of all, shouldn't be able to wear Legendary Plate Armor and weild a powerful sword. And even if you could make such a character, why do all of the enemy heroes only hit you with arcane arrow??? AI deficiency? Seems like they balanced a lot of this with encumberance--limiting what you can carry based on strength. Also, the monsters seem a *lot* more buffed. Champions should be more powerful than any other unit--especially at higher levels--but not god-like. I have no idea if the enemy heroes are any tougher, but they should develop much more than they did on WoM, and in the very least cast area-of-effect spells or crippling single-unit spells.
I'll take a spin when I get the beta and see if my opinion changes. What difficulty setting were you playing on?