The reason why some people are rating is down is because even on the lowest difficulty, the game is pretty hard, took me several tries to beat it. You can beat the lowest difficulty by stacking needlers, one or two frost towers and some axe towers and then upgrading those. Place them near the entrance to the base and upgrade them. Only upgrade the needlers once for a while because one level 2 they can hit air and ground and upgrade the axe to 3 or 4 if possible. You can beat the game this way but you won't come out perfect.