Thanks rafaelrq, I hope you enjoy the campaign
Now deepstrasz, I'm sorry you didn't enjoy it, but I would suggest that you give it another try on Hard mode. Hard mode did get indeed more attention and there are extra Boss fights and secrets on that difficulty.
Also keep in mind that many issues such as the Sea Giant and the Garrison/Guard Tower problem have already been fixed by the time of your post (check the changelog)! - I've tried many times to fix ranged Footmen dealing damage to crates, I am still working on that problem.
Let me answer some of your other problems one at a time:
1. The missions are all available from the start so as not to force players to go through everyone of them. Maybe someone just wants to try the 6th or 9th chapter. The choice is theirs.
2. Upgrade placements are a bit disorganized indeed (like the bounce shot) but the solution for that would have been a new building, and I didn't want to cluster the tech tree even more. In the end, I don't think it's that bad and most upgrades can be found where you would expect them to be. The Bounce Upgrade cannot fit in the workshop due to a slot having to be reserved for the cancel button if something is being trained.
3. Some units would seem similar at a first glance but there is quite a lot of nuance to each of them. You were saying that the ranged Footman was similar to the Rifleman. If you would take a closer look, you would see that they are quite different ranged units. The bow Footman deals Normal damage which means it will deal less damage to units with Heavy armor such as Abomination but extra damage to units with Medium armor such as Ghouls. The Rifleman does exactly the opposite with his Piercing damage. It may not matter as much on Normal, but you have to choose your units more carefully on Hard. The extra units offer you the choice to vary up your play style, but you can do it just fine with the original ones.
I personally don't agree with you that the original units were interesting enough, but it's a matter of taste.
4. Spellbooks - these contain situational spells if you can spare the extra mana. If you are a more micro-focused player there are plenty of situations where using a Spellbook can give you the edge in a battle.
5. War Horses and Lieutenants - War Horses attack very slowly, have poor health and cannot upgrade their armor. Lieutenants are maybe 25% more effective than Footmen while costing 85 more gold with a longer training period. Even if you mount and upgrade them and they become more effective, when one of them dies all nearby friendly units are Demoralized, and Demoralized units die fast. Making more than 3-4 Lieutenants is a very bad idea.
6. All Generators are invulnerable, including any Red ones in mission 2. There was a bug where, due to upgrading, the Invulnerable icon does not appear, but you cannot destroy a Generator regardless. I will take your suggestion and prevent people from accidentally researching the same Generator twice, thanks for that
7. Medivh returning: that's intentional and was present in the original campaign, I didn't mess with that. It probably suggests that Medivh hears Jaina's opinions and this is how he chooses her as humanity's savior. Also Jaina can't mount because I haven't found any mounted Jaina models and my skills as a modeller are close to 0. If a model appears, mounted Jaina will be implemented.
8. The Paladin is a character from World of Warcraft. With the 1.8 update he has a few lines to say.
9. The boat is there to give you a bit of help not break defenses on its own.
10. Frozen Deathwave is intended to deal damage to your units, as stated in the ability's description. Holy Light costs more because it's more powerful than the original spell and Arthas can gain a lot of mana regeneration by the
end of the campaign.
Many thanks for all your feedback. I do intend to transfer the tech-tree to a PvP map once I am done with all the campaigns, but for the moment I am quite satisfied with the way it is. I'm sorry you didn't enjoy it that much, but I would suggest again to give it a try on Hard - things get a lot more interesting.