Have to echo some of the other comments. Unit costs ridiculous, the basics should be less to enable you to get in to the game and experiment. I click on buy even now I have enough andnothing happens.
Just completed, good game, very challenging in places needing a shift in strategy and several attempts to get it. Just mirror the other main comments about scrolling and having to reselect a building each time rather than being able to place multiples.
 "Waraxe"){kind=icon}
 "Kingdom Rush"){kind=icon}
 "Obliterate Everything"){kind=icon}