I like the concept, but there's a few weaknesses:
- I only used two buildings: Stealing and Basic. Just two big rows of those seems like a sufficient strategy.
- It's too tedious to upgrade the buildings. Let me group upgrade.
- There's no need to pause when upgrading, just let the game continue.
There is a bit of a balancing issue. Quite easy until Level 7. Can beat every level on Hard, thus have maximum upgrades. Fail terribly on Level 7 even with a variety of strategies. A big problem is that the towers don't get any special abilities until they are levelled up 3 times -- thus there is very little strategy in their initial placement.
It needs work. So far just placing a bunch of electricity towers at the start seems to work (went to level 6 then stopped playing). The buttons are a bit small, in particular the upgrade button is tiny. Tower descriptions should be clearer as to what they do. Upgrades shouldn't be so freely allotted.