This was really fun! The controls were easy to learn and I appreciated that I could press E or the number of the building to confirm the selection. The mechanics were easy to pick up on, but I think if I were to play this regularly, I would want some kind of feedback, or something to work towards. Unlocking more buildings, having a point where one map is conquered and I move onto the next one, or even just keeping track of a high score.
I think I'd also like to see a larger incentive to leave the "safe zone". Early on, there was some risk going to retrieve corpses to make more buildings, but at a certain point, I could safely stay away from the "front lines" for as long as I felt like playing. If there were some power up or special item that I could only get by going myself, it'd reintroduce the risk factor without making it a requirement, since there isn't really a "win condition".
I enjoyed the necromancer theme, I thought it was funny :)