Red Harvest is basically Yojimbo/A Fistful of Dollars/Last Man Standing/etc./etc., but of course Hammett was first. If you read it, try not to get too attached to any of the characters. This should not be difficult. Even more than in the stories, the Op is externally as hardboiled as they come, while internally introspective and self-loathing (well, as i. and s.-l. as a hardboiled detective can be). Definitely a winner, and a real standout as a first novel.
He followed up with the Dain Curse, which I didn't like as well. A lot of improbability and a resolution that is pictured in the dictionary next to the phrase "farrago of nonsense". HOWEVER, it does have some tangential interest in that a major section of the novel is set at a Temple of the Holy Grail, which appears to be something of a stand-in for the actual Hermetic Order of the Golden Dawn. Hammett even drops Arthur Machen's name. Machen was a member of the Golden Dawn (as were AE Waite, Yeats, Crowley and a host of others) and was something of a Dr. Jones Senior-style Grail nut. And, to mount one of my hobby horses, Machen's supernatural fiction had a strong impact on Lovecraft.
Speaking of supernatural fiction, those of us who pore over the old stuff know that Dash Hammett edited Creeps by Night, an anthology of supernatural fiction published in 1931, two years after the Dain Curse. Contents included Lovecraft's "Music of Erich Zann" and tales by two members of Lovecraft's Circle: Frank Belknap Long and Donald Wandrei.
And now that you've been so patient, a duck that's hung like a horse.