Full review on RPG.net, based on the physical book. Includes using CC&C for the D&D "Starter Set : Lost Mine of Phandelver": https://www.rpg.net/reviews/archive/19/19119.phtml

Castles: The castle walls should work just fine for a "close up" of a castle for encounters such as speaking with the city guards, sneaking inside the castle, an NPC encounter inside the castle walls, that sort of thing. I was sort of disappointed that I couldn't make a generic castle (with the four corner round or square towers, walls between the towers, and a drawbridge), even with the castle walls in the Town and Taverns Battle Mat Books. Miniature skirmish gamers can still use the battle mats for that attack on one side of the castle.

The room maps in the set are suitable for not just castles and NPC town locations, but as generic rooms for RPG'ings. Breaking down the more functional rooms we have:

Throne room and school. School could be used for a smaller church. Castle gate complex with drawbridge. Large dining room with kitchen, and royalty or merchant quarters. Can be used for an inn or tavern. Barracks and armory, with castle wall courtyard. Castle courtyard. Each two-page spread can be used for the outside or inside of a castle wall. Large two-story library or academic area. Single pages may be used for smaller libraries and ballroom area. Four-story wizard's tower. Single pages may be used as individual rooms, like I've done for the D&D adventure. Generic rooms. Impressive spiral staircase and master bedroom, and smaller rooms. Maze hedge. Garden or upper-class park. Sewer complex. Plus four-pages of blank tiles for your other maps.

Crypts: And, for town and other encounters, this two-volume set has churches as well! The largest church is a two-page spead, with the services on one page, and entryway, office, and smaller services area on the other. Thus, you can use this two-page spread to make smaller areas of worship. Another page has a half-page school room that can be used as another services area in a church room. In addition to the church, the set has a double-page graveyard. As for actual crypts, we've seen the large single-page one-room crypt, with the adjacent rooms that have a crypt. One volume of the books has a double-page spread with an inner hallway. One of the volumes has generic rooms with spider webs on one page, and a single webbed room that can be used as a forgotten temple or altar. The other volume has two pages of webbed ruins and caverns. Unfortunately, these two pages are pretty much the only ruins in this set, although Coast of Dread has two ruins maps, and the "Add-On - Wilderness" vinyl clings has a page of ruins.

Caverns: As said earlier, some of the cavern pages can be used for generic outdoor hilly encounters. "Castles, Crypts, and Caverns" has sixteen cavern pages, with six, I would say, usable as outdoor dry terrain. Cave entrances, underground rivers, underground lakes, cavern fungi, cavern and ruins, it's all here.

Conclusion: The books are fine for castle RPG encounters, as well as adding more generic fantasy rooms and caverns for your dungeons. Some cavern maps can be used for outdoor hill and mountain encounters. For anyone new to battle mats, I would suggest the RPG Toolkit, Box of Adventure, Book of Battle Mats (The Dungeon and Wilderness), and Big and Great Book of Battle Mats series.