It's just a pity that the story is rather weak, reworking a lot of elements from Cigars of the Pharaoh (made even more obvious by the character of Allan appearing in both, though his appearance in the former story was added during the later redrawing) and including some contrived circumstances and missteps to drive the plot. It's also the shortest of all the complete Adventures, with the album edition including four extra full page panels to bring it up to the standard 62-page length.
Some of this is down to the circumstances of the original publication with paper shortages in wartime Belgium reducing the space available for the strip in its new home, Le Soir newspaper and its children's supplement, Le Soir Jeunesse, which disappeared midway through the adventure's publication, moving the strip to the main paper. With Belgium under Nazi occupation it's natural that the series would try to avoid local controversy and even play up to the occupying authorities with the most obvious sign being the inclusion of a Japanese police detective despite it making no sense whatsoever that they would be investigating drug smugglers in the Mediterranean. It's less clear if this is the reason behind the oddness at the start of the story when Tintin meets Thompson and Thomson who are investigating a counterfeiting operation which appears to have ties to one of the smugglers but which is then never mentioned again. Had Hergé planned a story based around counterfeiting only to have it blocked by the wartime censors because of real life plans to destabilise enemy economies? It seems a little fanciful that the initial scene made it as far a publication, both in the original serialisation and in the wartime collected edition, but it's curious as to why this whole concept is introduced only to be ignored. But instead the emphasis is on drug smuggling.
Tintin finds his way into the plot when Snowy discovers an empty tin with a torn crab label and later the Thom(p)sons show him the possessions of a drowned man with the rest of the label upon him. This also attracts the interest of a Japanese man who tries to communicate with Tintin only to get captured. Tintin could easily have been put off the scent, as indeed the Thom(p)sons are, by the crew of the ship Karaboudjan, but instead they first try to kill him and then capture him. It's a somewhat contrived scenario to get Tintin into the plot but it has the side-effect of introducing him to the ship's innocent captain, the drunkard Captain Haddock.
Haddock was only intended to be a one-off character in this story but it's easy to see why he rapidly became such a recurring feature. His fondness for drink is at its most exaggerated here, with dangerous consequences such as when he gets drunk in a lifeboat and decides to burn the oars for heat or later in the desert when he starts fantasising that Tintin is a giant bottle of champagne - and attacks him in the deluded belief he is opening the bottle. Subsequently Tintin has a nightmare of turning into a bottle with Haddock attacking him with a corkscrew. Haddock's drinking does prove to have his uses in making him a fearsome fighter at critical moments but it can also make him a blunderer. Fortunately, the epilogue sees him overcome the alcohol and give a talk on the subject on the radio - only to be taken ill drinking water. Beyond his drinking, Haddock is a loyal ally to Tintin and far more use than the Thom(p)sons, making for a strong double act. His habit of shouting all manner of words as a substitute for actual swearing is actually quite endearing, making for an overall rounded fun character with lasting potential.
As noted above, the plot isn't terribly original. It involves criminals smuggling opium inside seemingly ordinary, everyday objects - in this case cans claiming to be crab meat. There's a stay with elements of a colonial elite. There's action at sea, in planes and in the desert of the Arab world. The smugglers are being led by criminals that include respectable figures in the destination settlement. All in all, this adventure is highly derivative of Cigars of the Pharaoh and although that adventure may have ended serialisation over six years before this one began, its presence as an album (which remained in print during the war) means that the recycling of elements can't be dismissed as a standard technique by creators who never expected all their work to be available simultaneously.
It's a pity that such a significant entry in the series should be so be an inferior reworking of elements of an earlier tale. Captain Haddock is a delightful creation and a fine addition to the recurring cast but otherwise this adventure is one of the weakest of all.