This is commonly regarded as Edgar P. Jacobs best work, another reviewer describes it as being dated, and yes it is definately of its time, but this is no bad thing. It has the look and feel of a 1930's B/W thriller, The comparisons to Herge are obvious, Jacobs worked with Herge during the Second World War, and essentially taught Herge how to use colour (the pre-war Tintin books were originally b/w). (The 2 men eventually fell out when Jacobs demanded a joint credit for "Prisoners of the Sun" at which point he went his own way and started Blake and Mortimer) Jacobs skills with colour comes through in "The Yellow M", it is strong and rich, pages 27-30 illustrates this perfectly. He is also an excellent artist, like Herge he uses the ligne claire style (my personal favorite style of Bande Dessinee), he also shares Herge desire for perfection, just look at frame 2, pg 14, anyone living in London will know thats Fleet St instantly, you could easily find the exact point that that picture is based in 2009.
As other reviewers have said, this work lacks humour, when you combine this with Jacobs willingness to include lots of dialogue, with huge text boxes, it becomes a bit of a slow read. Herge always did this better providing interesting supporting characters,(i.e. pg 23-24 of "The Red Sea Sharks", where Herge does a massive info dump, made paletable by the humour of Captain Haddock struggling to stay awake). This is all the more important when you consider that both artists use a bland leading character so that the reader can put themselves into the adventure, regardless of their own personal background. "The Yellow M" suffers from having 3 bland leading charactors, Blake, Mortimer and Kendall, and this makes the storytelling a little dry (the excessive use of narrative text boxes adds to this).
Nevertheless despite these criticsms, this is an essential purchase for any Bande Dessinee collection and a rollicking good adventure story.