It looks pretty good. As far as I can tell, the entire Royal Family is there: Blackbolt, Medusa, Maximus, Crystal, Karnak, Gorgon, and Lockjaw. I haven't seen Triton, but I'm pretty certain that the character has been cast.
The trailer shows Maximus agitating the Inhumans and getting everyone read for a coup against his brother/their king, Blackbolt. For his part, Blackbolt looks constipated a lot. Don't believe me? Check this out:
Maximus is played by Iwan Rheon. You might know him from "Game of Thrones," but I love him for his portray of Ash Weston on "Vicious." He was also pretty good in "Under Mild Wood." He certainly gets the most dialogue and screen-time in the trailer. Then again, he's deposing a silent king so that goes without saying.
Not only will the Royal Family have to contend with Maximus and the mutinous Inhumans, but they'll find themselves running from the forces of humanity on planet Earth.
I'm interested in the show, but seeing Lockjaw in action is what sold "Marvel's Inhumans" on me!
You can watch the entire trailer here.