I Loved it so much I finished it twice
took me a few attempts to finish it,
Most important modes to win the game with seem to be Normal to regain your stamina quickly & Defense in order to heal, Drill is good for the 2 bosses at the end But otherwise it runs your stamina out to fast.
I think it would be good if it was not only longer But you had different fight areas also, Like every 12 waves you fought a a new place.