There is exactly the right amount of personality in the worm, apple, rock, hole puzzle. The slightly squished expression when facing a wall, x__x eyes from spikes, general neutral expression of apathy to player commands, yet a faint sense of disappointment is conveyed when a hopeless situation is encountered.
Subway level is a good way to grind; If at least one unit goes for a walk ignoring enemies and reaches the safe zone, you get 10k, if you get all your units that is 15k.
This would be interesting from a tower defense genre style also, have the game elevate throughout the korea war, defending the bridge as different factions, then after peace is declared continue gameplay with people trying to escape the north being gunned down by your end game strategy. Then the reveal. Cartoon enemies would help the impact.