Well, I really liked the execution so far. Very nice campaign. Pros:
-Scarlet Crusade monastery interior design is just perfect. It really captures the religious and medieval ambiance well. I have high hope for this to be the best grace.
-Heroes spells are well-thought-out and nicely executed. I personally preferred Darion at so many missions. Ashbringer spells are well-balanced and nice. Yet another securing grace.
-Argent Crusade mission element is nice and well-grappled.
Suggestions:
-Techtree needs to be polished, imo. Argent Crusade units have just standard abilities of their respective races. I suggest adding different abilities to further carve out the techree. Also, what about adding racial, specific upgrade that affects all units at a high cost? This could be each unit gaining increased regeneration and attack damage against undead (since their primary goal is to eradicate undead). Also, Gryphon Rider is not benefitting from attack and armor upgrades; that was a minor bug. Also, I think paladins should be granted extra more spells; these could be "power word" where he casts autocast spell that increases damage and resistance, and maybe single-unit "resurrection". The promotion cost of footman to paladin can be increased to balance with this. I think archers should have active ability of elune's grace that increases the movement and attack speed that makes them even more effective. Same goes for Scourge and Scarlet Crusade; where the new units could be added.
-As for heroes, I think Kel'thuzad's model should be changed. He is Archlich after all and being given a purple lich model is underwhelming. I think demi-heroes should be resurrected at altar after completion of Naxxramas mission (and yeah, they also don't benefit from upgrades; a minor bug). OR each mission completed with them surviving can be rewarded with enhanced abilities and power (and, specifically at the last mission, what about making them full heroes?).
-Naxxramas mission should have more boss fights involving Cult of the Damned. The halls kinda felt empty. Also, what is the use of killing 'strange creature' in this mission? I thought killing all of them would gift nice item or artifact. Also, some boss fights should have more difficulty especially Scarlet Crusade xD. So far, these are my thoughts. I hope you will enhance it even more and make it perfect. Good luck!