Some quick impressions:
-Morale is a more important part of the game. There are now more skills, units and artifacts to increase morale, even for neutral units. Also, enemy units have morale, which is a big innovation. Morale changes during the battle - negative effects, for example, decrease morale!
-Critical Hit chance is shown in unit description now, and many effects and abilities, even skills, change this.
-Certain spells have been majorly re-vamped. Battle Cry, for example, is a mass spell even on level I.
-There are a lot of unit abilities that come into play when a certain number of the unit has been destroyed (Barbarians alway inflict Critical damage after they are halved, Swordsmen get Evasion, Lizardmen/women get new talents, Gobot worms can multiply). This makes the battles more interesting, and moreso makes gives you - or your enemy - a chance to come out on top even after losing many units.
-Unit avaliablity, most likely thanks to listening to feedback at forums, is less random. You can guaranteedly find certain units in certain places, for example Inquisitors - for whom there is much demand for - are for sale in most temples. There is even a Green dragon you can recruit fairly early in the game.
-Similary, most likely after listining to us non-loss game maniacs, you can do the training mission without losses since you get Paladins for your army (and you fight ents, not a dragon).
-Followers are more versatile then wives, and give unique bonuses, some even change during the game.
-Sadly I find the main plot and the quests less diverse then KB-The Legend. Most quests are simply headhunts to kill an enemy hero. There are still complicated quests and tricky ones with multiple outcomes, but far less then in the original game.
-Hint: When choosing your Dragon pet, most give average bonuses like +1attack, +5 Mana, etc. The light blue one, though gives +1 initiative to all animals in the army! This also includes dragons!
-Many units have been tweaked and generally, they are more durable and have more then one uses on the battlefield. Most Level 4-5 units got HP increase (Royal thorns are real monsters with their 360 HP!), some too powerfull units have been de-nerfed (Cannoneers have lower initiative, dragons are less fast) and most level 1-2 units got new abilities that make them usefull even in battles against level 4-5 units (Fairies can mark targets for archers, lake dragonflies can paralyze enemies, Pirates can evade attacks, werewolves can increase their numbers similar to ghosts against humanoid enemies).