Thrashball is a nice Horde map. You have a solid base, but you still have to watch the little hallways, and if you try and camp way up top, enemies will spawn at the Mortar. You can also try and knock down the scoreboard on bosses, though there's always someone shooting it down during wave 1.
What I don't like about Overpass is that the base is tough to defend during bosses. They get up there easily and it's a death trap. for the other 9 waves, it's EZ mode. You have a good base and if you stay low, all the enemies just funnel up to you, and you have great cover.
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Donny: Are they gonna hurt us, Walter?
Walter: No, Donny. These men are cowards.