A great concept lacking any real mid-section of the game. Charles quickly no longer becomes a threat and the only issue is not going too far from your train. While the side quests are supposed to do this only some do and there is more than enough free scrap (the resource needed for upgrading and repairing) to only do the easier quests.
The game could gain an extra half a star just by making it so that Charles takes more damage as you collect more eggs.