Thank you for the feedback. Initially, I wanted to implement some units linking to allies or multiple enemies/ other enemy fields. However, the 10 days weren't enough to achieve this on my own.
Upgrade strength really depends on the unit right now. During playtesting, I felt that upgrading AOE (esp. Dead Pharaoh) or Ranged (esp. Pharaoh, the best unit in the game) was best, sometimes more important than new units. But I linked the game more with first focusing on building your army and later upgrading it. But that depends on individual taste, I guess. Also, there's for sure room for balancing improvements, as I discovered a bug on the last day that required me to rebalance everything within only a few hours.
Anyway, I'm glad you still liked it. Thank you!