As a whole, the Dusk Trilogy of the Atelier series concerns the world of Dusk and its inhabitants. The world itself seems to be dying in a number of ways- seas are drying up, lands are becoming barren, and there appear to be new dangers every day. If this sounds dismal- it kind of is. The world of Dusk is probably the darkest of the Atelier worlds. The art direction and stories of this trilogy feel grittier, despite still dealing in a lot of anime-flavored tropes and styles.
On a personal note, this trilogy is my favorite of the Atelier series that I have gotten to experience. As a horror and drama fan, this game appealed to my tastes in a strong way (despite nothing involved to actually be considered “horror”). While I have my qualms with how it was handled overall, each entry felt strong in this trilogy and the mechanics were sound. The art direction- now in the hands of an artist named Hidari- also veers toward the more ethereal feeling that the games have been sticking with since.
While the Dusk trilogy is not quite as lauded as the Arland trilogy or as current as the Mysterious trilogy, it weaves an intriguing tale that stands apart from the usual fare of the series while retaining most of the elements that make the Atelier games so unique and engaging.