No fair I wasn't invited
I think the boss fights with huge creatures is a nice touch, but no more than that. It has no impact on multiplayer, which is what I'll be looking at. Artifact sets are fine, just not important at all unless they're readily gotten. No initiative is OK too, it's something I can deal with. The initiative system, while fun and unique, can be dramatically random - e.g. whichever hero moves first and second can have a huge impact on the battle.
A convenient spellbook is great. Selecting a town and hero not so great ... towns have always been easy to select, while the obvious method to open up an inventory is to highlight the hero and press "i", so I don't get the point behind the click-and-drag.
Finally I discussed it with one of my brothers and we've both come to oppose the city / mines change. It makes turtling easy and harassing difficult. If it's possible to hold a castle easily while the main hero is off adventuring, then you lose almost nothing if someone attacks you without enough force to take the castle. In Heroes 2-3-4-5, the defender would have to hole up in the castle and concede all mines outside it; in Heroes 6 the defender would be perfectly alright. I don't see how this is a good change at all.
Concrete example - take the Heroes 5 map Mystic Vale, which is a classic 4-corners map where there's one player on each point of the compass (north, south, east, west) and lots of goodies in the middle. North is connected to east and west, etc, by means of a guarded path. Since the guards to the middle are quite strong, this guarded path becomes the focus after players have cleared out their starting areas. Clearing this path happens in the second week.
So say the player at south (Haven) makes the blind choice to go west, while the player at east (Dungeon) makes the equally blind choice to go south. The east player arrives to find south's lands unguarded, but he can't take the castle - it's a castle with static defense, Blood Furies can't cross the walls, he doesn't have enough spell points, his opponent is going to split his creatures into 7 stacks, etc. Even so he can cause major havoc to south by taking all his mines and disrupting his transport chain. The higher the difficulty, the worse this hit is going to be, especially since east will be using at least two heroes to wreak this havoc (the main hero and the transporter).
In Heroes 6 however there's nothing to gain from such a hit. East can't claim any of south's resources unless he parks his hero on a mine, which is stupid for a main hero in the second week. Parking a transport hero on a mine brings really low return (you get +1 resource for 2500g ... what?) and means as well that the supporter isn't chaining troops. East can still take obelisks, +1k experience buildings, +1 to [insert stat] buildings, etc, but east can't hurt his opponent. South has plenty of time - right until a couple of days after the start of the next week, before the new weeks' population arrives - to come back and defend his power base. Therefore south can ignore east's hero when it shows up and push on westward.
I don't see how this is a good change at all.
I'm a hypocrite because I suggested that all life is sacred and should not be wasted without good reason.