Interesting idea, you've got to make do with the placement of the towers and learn when each one is most effective. Definitely difficult, but did much better after a first learning round, and it was satisfying to get a handle on the concept.
I'd like to see it with a longer path and more towers available (maybe it takes longer to run between further towers?) If enough got past the first two towers, there wasn't always a lot you could do to get the situation back under control.