Ok while making these maps, consider what might in any way hurt an army, including other units that might be overpowered. Superfrog's got some good points, and even if you're making maps to play on "for fun" I can guarantee I won't be smiling while your hydra is swimming up and down the river chomping on my Romans
Ruined path looks very fun. No large issues here except that the start zones are very far away from eachother. Most of the battle will likely be spent trying to move soldiers towards the action. The center area looks nice, though I don't get why the lava's there.
Anyway, thanks for letting me nag you with my OCD map tips