It's a good start, and there is something pretty fun to slamming down footmen. I don't feel I have enough time to move at all though, because I have to spam footmen as fast as possible. Also, because I can't place footmen where a goblin is, I inevitably get pushed back and back until I die. Perhaps if the footmen were heartier and cleared a space around them, you could pushing back against the relentless goblin hoards. Some variations in the hoard size would be nice to, they could come in more or less intense waves.
Nice work, I think this could be a simple but fun project, given a bit of polish.