This is, unsurprisingly, a retelling of The Magnificent Seven, which is itself a retelling of The Seven Samurai. There's a good reason the story has been told so many times: "group of heavily outnumbered but highly skilled warriors defends village from invading force" will always be a great premise for a story.
The twist here is that the titular seven are all dyed-in-the-wool villains. They consist of a demon raiser, a necromancer, a vampire, a pirate queen, a war god, an alchemist, and an orc chieftain. They're all bad people (though some are worse than the others - the other six all uncomfortable to be working alongside the alchemist), and they're all their for their own selfish reasons, but they all intend to do their best to save the inoffensive village with the bad luck to sit in the path of a fanatical theocratic empire.
The story that unfolds is pure popcorn fun. Not only do you get the fun of seeing what clever tricks/horrifying crimes they do to stop the invaders, at the same time all seven are plotting against the other and looking for the right moment to both defeat the invaders and come out on top of their allies.
This isn't a book that'll change your life, but it's very much a book worth the read if what you are looking for is entertainment. And even though none of the seven are good guys, you still have reasons to root for most of them.
Props to the author for a good gender balance. The demon raiser, necromancer, pirate queen, and orc chieftain are all women. The orc in particular, upon arriving at the village, asks first thing why the stupid humans are only training half of the people as fighters and immediately sets to training the women. The captain of the militia women (Penny, later dubbed "Red Penny") is one of the few side characters and by far my favorite.
Warning for graphic violence (these are very bad people) and violence against animals (again, bad people). No rape, though, which was a relief.
Comes out on August 10. Thanks to Angry Robot for the ARC.