As mentioned earlier I too was put off by the top of the main image being incomplete but ever since then this has grown on me and I can appreciate it for what it represents.
Granted, it's very different to the majority of U.K. steelbooks in that it is not an easy uncomplicated image of the main actors in the drama or of a recognisable image from the film and I appreciate that people may be put off by this . . .
Not that anyone is interested but my thrupence worth of opinion is that the main image is akin to the portrait in the attic in the wonderful Oscar Wilde story THE PICTURE OF DORIAN GRAY (and the later 1945 film of the same title) where the main character has a portrait painted and expresses a wish to be young forever and that the portrait should age instead (the old story about selling your soul to the devil in exchange for whatever).
What happens, however, is that although he does indeed remain young all his corruption and ill-deeds are represented in the portrait to the extent that the original portrait of a very handsome young man becomes totally unrecognisable and more and more repulsive until by the end it is barely human. No ending available in case anyone is not familiar with the book / film and I wouldn't wish to spoil the 'surprise'.
IMO the steelbook image parallels this notion in that the lead is likewise very handsome, not aristocratic as in "TPoDG", but very successful and well-paid instead - a totally recognisable figure as one of thousands of 'yuppies' on both sides of the pond in the1980s with the Armani / Valentino / bespoke suits et cetera.
His colourful personality, hedonistic lifestyle and various misdeeds, leading to murder, are represented not by ageing of this 'portrait' on the steelbook but by the shredded expensive suit and the expression on his face - his corruption, and the murder committed, have turned him into a shadow of himself, his features, apart from mouth agape, almost completely unrecognisable as if frozen in a rictus of agony as the flames of hell consume him . . .
A crock, maybe, but that's my take on it
If they can put a severed forearm on the front of the forthcoming SAW steelbook and a Mickey Mouse shadow on the front of the SAVING MR. BANKS steelbook then why not this . . . ?
EDIT 23/10: Of course, instead of the above, it could be one of those mad triumphant laughs . . . cue Spaghetti Western music . . . and if you've seen even one of the many in that genre you'll know what I'm on about.