1. Should not have fixed start locations for better gaming experience and not knowing where each player is every time (this last one in case you decide to make more than 1v1 maps, which I hope you will). I'd also not mark anything on the map either, especially the enemy's position.
2. I don't think it's necessary to have a quest. Also, when you win, it says victory or quit campaign not game.
3. I guess, no refund percentage for cancelled buildings (walls too).
4. Maybe, just maybe replace the soundsets with the original Warcraft: Orcs & Humans ones?
5. Funny thing is that even though you don't have rally points, you can select the worker inside a building and set waypoints. You can do so even before holding the SHIFT key.
6. You can also select more than 4 units at a time.
7. I don't think you should keep the flat terrain aspect.
8. You could also add ground animals, unselectable like that raven.
9. Sometimes the road wants more road near the place where you want to put another piece. Sometimes (happened between a wall and another building just south of the main building) it doesn't want to be placed in some spots if another piece isn't to its left or right even though just up of it there is road.
10. I really don't know the armour and damage types for the original game but I guess it's OK. I don't remember if a catapult actually dealt its whole damage to a building and so on. Did a catapult not kill a knight/wolf rider from one shot without any upgrades on any of the units?
11. Heal wasn't autocast

You really need to decide whether you want to make it as close to the original or a hybrid of that and Warcraft III. I suggest adding Rally Point to training buildings too if you don't mind then

12. You need to find a way not to overlap the text of cannot build there with whatever else there appears on the screen at the same time.
13. I'm not sure Rain of Fire's area of effect and wave delay speed are accurate. Also, I remember the fireballs not falling all at once, if I'm not mistaken of course.
14. I didn't check the music but I hope every faction has all the songs from the original game playing one after the other

15. You need to create a Random option. It's not hard, just replace Undead with Human and Night Elf with Orc using triggers.
16. The catapult and raider's icon positions in the Barracks are not the same as the ones for the human catapult and knight.
17. There's a space between the Warlock's spiders upgrade and the other two. The Wizard upgrades aren't positioned like that.
18. I don't remember if the scorpions have teamglow but the spiders do. I don't exactly remember if in the original game either of them had that. I guess not. Same goes for Daemons and Water Elementals.
19. Cloud of Poison is inaccurate. It is supposed to wander by itself damaging units. I think you could simply make it a unselectable timed unit with permanent immolation at the chosen/cast location.
20. I remember that in the original game, you could still hit and units would still acquire enemy units with Unholy Armour on.