For a picture book (and even for a short comic book style graphic novel obviously and primarily meant for children), Raymond Briggs' Fungus the Bogeyman is actually in many ways rather sophisticated and involved humour and narrative-wise. And although I do believe that especially boys will likely and perhaps even definitely enjoy much of the presented text and be especially captivated with and by the at times rather disgusting, overtly ribald potty-type humour, I do not necessarily think that they will all that easily understand all or even most of the more sophisticated allusions, parodies and such (and I equally do warn parents who are considering reading Fungus the Bogeyman with or to their children to actually consider at least skimming the entire book before using it for their little ones just to make certain that they themselves do not end up with both narrative and illustrative surprises they might personally consider inappropriate). And as such, I personally would also not generally consider Fungus the Bogeyman as a book for all children, but most suitable and enjoyable for children above the age of seven or eight (but there is really no upper limit for Fungus the Bogeyman as teenagers and adults who enjoy graphic novels, parodies, satires and coarse, crude humour type of offerings would likely also find their proverbial funny bone tickled).
However, as much as I do enjoy both the concept and appreciate much of the humour, I actually remain a wee bit disappointed with and by Fungus the Bogeyman. Now I do find the societal reversals of Fungus' underground domain and the everyday human world above ground both entertaining and massively appealing (basically distorted mirror images of one another with, for example, Fungus and his wife relishing a slimy and cold bed whilst the humans above ground would of course desire their beds to be warm and dry). But that all being said, the constant and continuously recurring anally, body fluid and excretions based humour does tend to feel and become rather overly exaggerated and overused (even to the point of wearing more than a bit thin and thus no longer even being all that humorous to and for me, and mostly like a buzzing mosquito, somewhat annoying and recurringly tedious).
And even considering that many children do seem to massively relish and cherish humour based on bodily functions and liquid excretions, I do have to wonder whether the massive amounts of the latter occurring in Fungus the Bogeyman might well end up being potentially distracting and even too much of a "good thing" (so much so as to even jade and feel dragging for children who usually enjoy this type of humour, these types of jokes). For while Fungus' world and his daily life are indeed often minutely, engagingly and even in a strange way beautifully described and depicted (and the accompanying illustrations are gorgeously drawn and actually, amazingly sparkle with their very and often intense general ugliness), really and truly, for and to me, the constant and ever-present referrals to farting, vomiting, grottiness, slime, mould and the like does tend to become rather frustratingly dragging.
But even with me being a bit disappointed with and by Raymond Briggs' Fungus the Bogeyman as a story, I would probably be giving it a high three star ranking (and not the two stars I am at present considering) if the textual presentation of the book were even somewhat easier on my aging eyes. Because fact is that I have to use my strongest reading glasses throughout and still be constantly squinting, as especially the font size of the printed, of Biggs' presented text is so cramped and so minuscule in size to make easy and comfortable perusal nigh impossible (I have actually had to reread some sections more than a few times because my eyes accidentally kept missing and skipping entire chunks, this also being a further caveat for parents reading Fungus the Bogeyman with or to their children, and perhaps also a potential issue for recently independent readers attempting to read Fungus the Bogeyman by themselves, as they often read better and easier with larger and bolder print). And I am quite frankly (and personally) getting more than sick and tired of rather too often encountering especially picture or comic books geared towards children that have a presentation style that seems to not at all take the importance of visual comfort while reading into consideration and seriously enough (as well as the potential eye strain an overly small font size can often and even likely cause).