The first surprise - ah, hell, it's the only surprise, let's be honest - is that Mr. Peabody & Shermanis not terribly good, but it's not terribly good in the way that DreamWorks Animation features tend to not be terribly good. That is to say, it's not a hell-spawned devouring nightmare that leave nothing but charred remains of the characters first premiered in 1959 during the "Peabody's Improbable History" segment of producer Jay Ward's variably-named Rocky and Bullwinkle Show, mocking all that is good and decent about animation that actually tries to be creative and intellectually engaging simply by the fact of its existence.

Instead it's just another damn DreamWorks movie with vaguely unpleasant, angular human character designs, a severe problem with eyes that look like glassy marbles with no personality behind them, bright colors over every vaguely rubberised surface. It does almost entirely without pop culture jokes, which is great, because the ones it comes up with are unfathomably dated (Zumba! Planking!); instead, it makes do with a number of fart- and shit-related jokes that makes me realise quite suddenly how much such things had been slowly disappearing from children's entertainment. Also, if you are looking for a reason to proclaim that the movie has brutally violated the heart and soul of the Ward cartoon from 50 years ago, you can hardly do better than point to the gag where it looks like the Trojan Horse is crapping out Greek warriors.

It also does mostly without gratingly obvious celebrity voice casting, the single most recognisable member of the cast probably being Patrick Warburton, who at this point counts more as a good-luck charm for animation casting agents than anything else; Stephen Colbert, Allison Janney, Mel Brooks, Lake Bell, Leslie Mann, and Stanley Tucci are among the other folks in the cast, none of them obviously there for their marquee value. Which isn't the same as saying that the cast is necessarily good; but they could have gone to some much worse places than they did. For which it is well to be thankful.

Anyway, the film itself, a profoundly difficult thing to discuss in any way; too dull and mediocre to be interesting or interestingly bad, it is the most product-like piece of studio product that I have watched in what feels like a long time. We are first introduced to the world's smartest dog, Mr. Peabody (Ty Burrell), who quickly sketches the details of his life: he is the adopted father of a human boy, Sherman (Max Charles), and to ensure the child's education, he has invented a time machine called the WABAC. The two visit historical events and learn from them, while modestly or immodestly interacting with the historical players; and now Sherman is about to attend public school, where his inflated knowledge puts him at an academic advantage but a profound social disadvantage. Having gotten into a fight with tiny queen bee Penny Peterson (Ariel Winter) on the very first day, Sherman's future with a dog father is called into question by shrill social worker Ms. Grunion (Allison Janney), and hoping to quietly paper everything over, Mr. Peabody invites Penny's parents (Stephen Colbert and Leslie Mann) over for an exquisitely prepared dinner. During that dinner, Sherman and Penny end up traveling into the past and she gets lost in Egypt; thus an adventure begins, during which the adoptive father learns how to be more generous with his affections and allow the pleasant messiness of family life to creep into his immaculately composed domestic situation.

It's difficult to say which is more vexing: the strangely insistent "learn how to be a closer, more loving dad" theme, which can hardly be of primary interest to the child audience that the film obviously presumes for itself, or the descent into clattertrap science fiction boilerplate about rifts in the space-time continuum that turns the film's final act into something that is neither funny nor heartwarming like the rest of it tries to be, sometimes even succeeding. Both, at any rate, suggest that Mr. Peabody & Sherman began production and ended it without any clear sense of what it was supposed to be about and how: certainly, the notion that it was actually just supposed to be a redone version of a cartoon whose cultural cachet is certainly not at a high ebb with the children of the 2010s is quickly dashed, given that "Peabody's Improbable History" never came within a country mile of the twee sentiment of this film, with its vastly more prickly Peabody and the strong impression that Sherman was his human pet, not his adopted son. Though I will credit the film with this much: it manages some fine puns in homage to the groaning, tortured set-ups that were the original's raison d'être, and one - "You can't have your cake, and edict too" - could have come from one of the best of the 1960s shorts. Even if the film stomps all over it by having a Sherman who flatly declares "I don't get it" instead of adopting the justifiable look of disgust and shame with which the original Sherman typically responded to Peabody's jokes.

Beyond its ability or not to evoke a brand-name whose natural audience would consist primarily, I suspect, of people in their 60s, Mr. Peabody & Sherman is otherwise a film of the most steadily generic sort, no doubt a good exercise for DreamWorks's artists and technicians (it is a bright film and not unpleasant to look at, though the characters are somewhat more grotesque than expressive - the backgrounds, however, are generally breathtaking, contemporary New York and Renaissance Florence especially) to keep their talents sharpened for whatever more prestigious and ambitious project is coming down the line, but not something that cares to indulge in more than the most basic factory-produced CG animation. On the whole, it is less obnoxious than the studio's 2013 Turbo, but also less idiosyncratic and visually bent than their last March release, The Croods. It is perfectly safe, fitfully amusing, increasingly dull as it goes on, and hugely uninspired in virtually every way that an animated film can lack inspiration (there's a montage that's actually rather neat, using flatter, more impressionistic color and shading than the rest of the film, but it mostly calls attention to how limited the creativity is anywhere else). It is the sort of film where watching it and napping through it are both more or less equally pleasant, and in both cases it's a little difficult to remember anything about the experience once you're done with it.