Kindle Unlimited used to have some really bad titles way back when it started, and it's still hit or miss sometimes, but I've come across some pretty good reads (in the "popcorn movie" vein, for the most part). Some that I liked (with the first book linked below):
Infiltration Game: A Think Tank Novel. Espionage/Thriller type book (think black ops team)
https://www.amazon.com/Infiltration-...sap_bc?ie=UTF8
Tier One series - same author as above. Two books out, one coming in December. This are same type of books, but I liked these a lot better than Think Tank one.
https://www.amazon.com/Tier-One-Thri...sap_bc?ie=UTF8
Black Fleet Trilogy - Military SciFi. Pretty good read.
https://www.amazon.com/Warship-Black...trilogy+book+1
Onset series - Urban fantasy, sort of. About a team that fights against supernatural beings. Something kind of like the TV show Grimm.
https://www.amazon.com/ONSET-Serve-P...+glynn+stewart
Bobiverse series - SF. Kind of an odd one. About a guy that wakes up after "dying" and finds himself as an AI for a ship. Fun series, but some people get annoyed by the character, he's kind of an ass sometimes. But I like the series.
https://www.amazon.com/Are-Legion-Bo...ords=bobiverse
Beneath a Scarlet Sky - this is an AMAZING book. WWII Historical novel based on a true story. I think this is coming out as a movie soon.
https://www.amazon.com/Beneath-Scarl...+a+scarlet+sky
Blood Defense - Legal thriller series. Not bad.
https://www.amazon.com/Blood-Defense...y+marcia+clark
The Neon Lawyer series - another Legal thriller series. Also not bad.
https://www.amazon.com/Neon-Lawyer-V...he+neon+lawyer
Jack Daniels series - Serial Killer/Detective series. Very good.
https://www.amazon.com/Whiskey-Sour-...+series+kindle