I think it was quite difficult, until I bought the boost tower. After that it was smooth sailing.
-Have an offset when dragging the tower, so that the finger doesn't cover the tower during placement. makes it much easier! (may require additional logic for edges)
-Maybe in the future allow a maze mode! I think it would require a snap-to-grid layout, which i don't think the current implementation implements.
-Air units and air towers/invisible units and invisible sensing towers.
-Races, each race has different towers and different special effects.
-Individual upgrades to damage/range (perhaps after the max upgrade?)
-Description of towers would be nice
-Space the towers a little bit, i tend to always grab the wrong tower. (perhaps there could be a build-tower button that opens up a scrollable menu that gives tower selection (can also place descriptions here).
-Ability to pause the game (for tower placement)
-Trial mode (would probably bring you the most cash)
-For some reason all my lightning buffs disappear
-When reloading the game, the boost tower disappears
-Can't upgrade the boost tower, had 15K gold and it still didn't work.
-That ice map didn't follow that pathing, is that intentional for the "slipping"?
I am quite impressed on your first project, did you use game studio when implementing this? or you did it straight up in c#? If so do you have any links that helped get you started (so i can take a look at them