Thanks a lot for such a detailed and insightful reply. Adding some of those answers as hover info would be quite helpful for new players.
Also if you add more variations to the towers and enemies, you'd bring this to a whole new level. With variations I mean stuff like towers that slow down, increase damage taken, stun, AOE, etc. and for enemies something like quick variations, tanks, enemies that are immune to some effects.
Some more about towers: Right now it's too much linear grow to towers. They all become practically "cover the whole map" range, while damage and speed are too linear, in short all towers become the same raw DPS output that is compared to the tankiness of enemies. If the towers would keep their range, while multiplying (instead of adding) their damage and speed, then they'd keep their character. (e.g. "this tower shoots fast, but short range", "this tower fires slow, but hits hard at a long range")
Overall I see some cool potential.