Goblin: generally nice shape. Though some extra details wanted. Something like skulls, feathers etc that will keep the general stylistics for all goblin characters later on.
Yeti: preferably look less human-like. Try to make him a more fluffy and hairy (might try including the face)
Gun: its one of the pearls of the model, it should be smth like real big medieval cannon in details, not like modern gun. http://2.bp.blogspot.com/-EADW6N1W8KM/T0K6unuHgAI/AAAAAAAABmg/kh6P8hr5D_Y/s400/IMG_7342.JPG