I played tower defense in WC3 all the time, which is what this map is like.
Anyway there are some bugs in it like the frist zombie level got a stack stuck and forever screwed up the kills remaining and when a level would end.
How to beat the samarui and suicide guys:
Samuri kill all the units in adjacent tiles when they attack (well they always did for me). So you need to defend against them with no other units around the defending unit.
Suicide guys can be killed by any of the ranged attackers. Simply bombard them until they die. When they start to get mixed in with other units you need to be positive that you do not kill them with anything but ranged attackers.
I thought the scenario was quite interesting but ultimately very very easy once you master the scout/ranged combo.
Basically, the mobs in my game always went for the same city every time. So i had a stack of ranged attackers inbetween where they would come from and where they were going, a couple of scouts to make sure I could see up to max range, and then would just snipe everything dead with rare exceptions.
Another uniquie unit to be wary of is the elephants. They would ocassionaly "move" my units when they attacked. So if you defend in your city, you can lose the city without a fight.
Also not sure why, but if your units don't fight for a period of time they slowly lose strength. My maceman got down to 2 strength thanks to my large army of ranged attackers when the mech tanks showed up. I went from 6 cities to 1 in about 3 turns but was able to hold that last city until I won.
I managed to weaken a unit to .01 strenght, which my maceman killed and he immediately went up to 18 or 20 strength and would then fluctuate depending on factors I didn't have time to test.