This campaign was really ok, basic, but nothing special. Personally, i like campaigns with complex stories and plots and deep/profound characters. Well, your campaign lacks in this point. The characters and the story are a little bit boring, sorry to say that.
What i liked the most is are your skills to make maps. Beautiful usage of doodads, nice terrain. Definitely well done!
Here are a few of my suggestions to improve the map. Think about it
In general
1) Make more side quest, and better rewards for your sidequests. Your maps are huge, thats good, there is enough space to add a few optional quests. Its easy to add new quests and it makes your mapps more interesting.
2) Reward the player for exploring the map. Many mappers do that. Put some nice items in hidden places. Let strong creepspots (remote ones, that do not have to be killed) drop items for you.
3) Improve dropped items: The main hero has the brilliance aura: Some units drop crappy mana-recovery items. These are so useless and senseless; Items in the
4) Improve the cinematics and the storyline: Leave the story like this, but make the cintematics longer, more interesting!! (We dont really know anything about the enemy: How about one or two an antagonist, an undead/demon leader that leads this undead invasion? How about some drama? Introduce a new important character that will be killed by the undead/demons? What is the purpose of the undead/demons?) Its your campaign, make the plot more interesting
Map suggestions
Map 1:
The first map (survive 10 minutes) is impossible to make without the goblin landmines. At first, i did not find them, and i lost. After finding them (10 meter away from the base), i managed to win. What the heck is the purose of putting the mines 10 meters away from the base?! Give the goblinmines directly to the hero and save the player some frustration.
-Usually, players get rewarded if they discover the map and look at hidden paths. You might add better items or hidden items in the first map. The items that you can get from the first map really suck^^.
Map 2:
Again, walking through the map wasn´t rewarded at all, just got useless potions. I liked the shop in the north though. I couldn´t find the optional quest in the first run. The game ended before i could find it (allies kicked the undead bases).
This map was by far the best map of the campaign. I really liked the concept of the second map, it is not just a run through. The idea is nice to have alliy forces that support you in the fight. You could use that map to improve your story-line, introduce the invaders, the antagonists, or stuff like that.
Map 3:
A little bit boring. I like the change of atmospheres though (Woods, City, barrens) Difficult in the beginning (which is good), easy in the end.
Map 4:
Amazing landscape and doodads, respect

! That map is really beautiful! The difficulty of this map was too easy in my opinion. (btw: Who is that fallen soldier in the beginning?)
Map 5:
Quite a challenge, but with the strong air units and two good healers, it can be managed. A hint. Put some strong towers (or some anti air) next to the gates. I just took my mass air, sneaked from behind and destroyed the portal.
In total, i give 3/5, because of the beautiful map design and the challenge in the beginning of most of the maps. Many things can be improved, that campaign has a lot of potential to grow/become better, which is good! I hope these suggestions help you to improve your campaign

.
Best,
SirGareth