The first game in this series, plus its corresponding anime series and movie, finally came to the U.S. in 2015 after originally being released in Japan 4 years prior. The second game(s) released in the U.S. in September 2016 -- taking a hint from Pokémon with two versions, Bony Spirits & Fleshy Souls. The third, updated version, Psychic Specters, is coming this fall.
In the first game, the main character is given the titular Yo-Kai Watch, which causes them to be able to see Yo-Kai -- spirits that cause all kinds of odd everyday occurrences good, bad, or just plain weird. A significant difference between this game and other monster collectors is that the player does not technically capture Yo-Kai, but instead befriends them by feeding them their favorite foods -- and is given their medal so that they can be summoned from the Yo-Kai Watch at any time.
Yo-Kai Watch has been losing steam recently after the third iteration didn't sell as well as the previous ones -- possibly due to Pokémon's comeback, the lack of creativity with some of the newer creatures, and the absence of true backwards compatibility between the games and the toys. The series also isn't nearly as popular in the West as it was in Japan, but it has found a pretty decent fan following in Europe -- with plenty of kids (and some adults) all over the world still enjoying it.
Although the gameplay is a little outdated being mostly touchscreen-based, the Yo-Kai Watch series is still a fun, and more inherently Japanese, alternative to Pocket Monsters.