Wave 17
12810 points
My strat - Don't get shotgun, go right for assault rifle, then get the three round burst gun, then get the most powerful machine gun, get barricade upgrade, then start dropping sentries in the choke point near the right side of the map. Stay as mobile as possible to get in close range (higher accuracy thus more cost efficient killing) and to repair barricades, especially early
Wave 20
Normal Difficulty
Score 16470
Basically same technique as last time, but actually skipped the three round burst gun. For some reason barricades only sporadically repair as the game goes on. Maybe you only have a finite number of complete barricade rebuilds. For next round, sacrifice the left side completely during the auto-gun phase. Also, drop auto-guns more judiciously. On the 20th wave, things go crazy, but at that point I had already bought a bunch of auto-guns that really I didn't need. Also, make sure to mix up light and heavy guns. Only heavy guns wave bullets on fast zombies that should be shredded by light guns.