Just a couple general things about all these places. Overall, Korea is fantastic at their parks. Each one had normal priced food for food that was decent to great. The ticket process is easy, each park had English options for maps and menus that were also in English. Transportation is a breeze. Everland is the only one that is not directly connected to a station and they have a free tram or you can take their bus from Seoul that is not very expensive.
The people at the parks at least act happy in their job and the parks are so CLEAN. Bathrooms are cleaned regularly. For rides where you can't bring your bags there are cubbies, some of them even have a door that closes until your little rollercoaster tram pulls up to it so no one can steal your stuff. Everything is well lit and it feels like they have thought of everything to make your stay enjoyable.
If you want more info or more specific directions and prices, check out this Korean Tourism site.