Why make a whodunnit movie at this point in time? The genre is completely exhausted and this example barely makes any innovations.
The answer is that this film is a vehicle for a thinly veiled critique of present day American society as represented by the Thrombey family.
Each family member is utterly odious, selfish, sycophantic, hypocritical and bigoted. At its heart is a latent neocon sensibility as most clearly represented by the almost fascist teenage grandson.
The only sympathetic member of the household is the nurse, daughter of an illegal immigrant of South American origin.
Ring any bells?
The final scene of the film, when the family is completely dispossessed of all their property and the nurse looks down on them from the balcony of their family home, could hardly be more explicit.
As such, the film is really rather obvious and clumsy in the exposition of its ideas.
As a result it’s rather unsatisfying.