5 StarsDescription: castles tend to have an original main keep and several supporting structures (moats, baileys, gates, castle town atmosphere).
Itinerary: These are historical treasures and it is worth the effort to go out of your way to visit them.
Audience: Everyone will enjoy a visit here.
4 StarsDescription: castles tend to be smaller original main keep with fewer or no surrounding structures. Some may be reconstructions of historically important castles and have a number of supporting structures or a castle town.
Itinerary: If you are visiting the area you should add this to your schedule.
Audience: Non castle fans will enjoy a trip here too.
3 StarsDescription: castles are reconstructions or ruins, have fewer structures, some may be small but are reconstructed well or have a nice castle town.
Itinerary: If you are in the area and have free time it may be worth the trip.
Audience: mainly castle fans and some people who have free time in the area
2 StarsDescription: small reconstructions with no supporting structures or interesting ruins. Commonly the reconstruction is just a simple local history museum. The actual reconstruction might be a mock reconstruction that was not designed after the original or they do not know what the original looked like.
Itinerary: probably not worth your time unless you have a specific purpose to go here
Audience: castle fans, people interested detailed history of the area
1 StarDescription: mostly ruins or poor reconstructions. Not oriented towards tourism.
Itinerary: not worth your time
Audience: serious castle fans who've visited all the better castles in an area