Seconding Shadow House, it's very good. Love how it transitions from a creepy slice of life to a full mystery/conspiracy with the characters ageing and progressing through the levels of the manor.
I would highly recommend anything by Fukumoto Nobuyuki. Kaiji is one of his most famous series about a dirt poor NEET in shitloads of debt that is forced into underground gambling in order to pay off his debt. Kurosawa is more down to earth than Kaiji and centers around a 40 year old failure who decides to chase the things he's always wanted - respect from his co-workers, popularity with the ladies, and a life worth living. Silver and Gold has a similar premise to Kaiji in that a down-on-his-luck man is drawn into the world of scam artists and gambling.
Although not drawn by him, Fukumoto's Confession and Seizon LifE are shorter series and I cannot recommend them enough. Confession revolves around 2 mountain climbers stranded in a storm. Fearing they'll die, one of them confesses to murdering the other's girlfriend - but the storm eases up enough that they are able to make it to a cabin for shelter. The manga then follows the tense few days while they wait for the rescue team, with the confession weighing heavily on both of their minds. Seizon LifE follows a man's quest to find out what happened to his daughter over a decade ago when her remains are discovered buried underneath a car park, racing against time as his cancer diagnosis has given him months to live.