Here's a bit of my feedback, mostly critical bugs, will do more chapter-by-chapter.
I'll start in general to mention my biggest complaint: No units?
I know in Kingdom Rush there are "Barracks", and then three or two units come out, in which you can then change the rally point as to where they can go and stay there to defend. This is what made Kingdom Rush great and unique.
Seems this campaign doesn't have it, so I was wondering...Is it planned? Or it's really hard to implement that it had to be scrapped?
Chapter One was great, no issues here whatsoever, good enough tutorial.
Chapter Two, the only issue I had here was the fact that the last wave was incredibly difficulty in comparison to the rest, seems the difficulty went from 100% to 200% all of a sudden. It might be my fault, I wasn't exactly ready, but I think it should be checked again to be judged better.
Chapter Three, have lots of issues on this one:
1. One time, the cutscene didn't work properly, Jaina just stood there near a recent skeletal corpse of an ogre. Luckily it continued just fine, so a visual bug more than anything, but still something I had to report.
2. The secondary achievement, where you must make Jaina reach Level 8...How exactly can I do that? The level has only two waves, I even tried a "No Tower" tactic, Arthas was only about 30 metres close, and Jaina never reached level 6 or higher.
3. It seems that despite completing the mission with all 20 lives intact, I didn't get any "stars" (Hence no lumber for the next mission), is that intentional?
4. One time, I had a skeleton archer get stuck right on King's Road, he was easily dispatched and the waves kept going though, so not a big critical bug but still should be mentioned.
Extra: Just a little nitpick; the bridge that leads from the village to Heartglen (I think that was the name) has trees to the north...Why? I thought this bridge would lead you to Heartglen itself, seems a bit illogical.