Over time, Pratchett's formula has shifted more and more from using dramatic plots set in Discworld, which provide a vehicle to reflect or lampoon real life concepts in a fantasy world, to reflecting or lampooning real life phenomena in Discworld and using that as a vehicle to carry a plot. Social commentary took the spotlight from narrative construction, but it worked out for a while, since Pratchett was good at social commentary.
But I think he dropped the ball on this one.
From the outset, the book focuses on the raging, fanatical following of the time honored, or at least time tolerated, pastime of Foot-the-Ball.
And so, from the outset, you have to stop and ask "wait, what?" Because this setting information comes completely out of left field. Over the course of the series thus far, Discworld has developed from a Terra incognita, full of the bizarre and mysterious, to, well, a place that's still bizarre, but to a far greater extent a known quantity. That such a major cultural phenomenon could pass completely under the radar thus far strains credibility. Over the course of thirty six books previously, football (not then called foot-the-ball) had in fact been referenced, once, in Jingo, for a one shot gag where a battle was reorganized into a game. This is a sign that football at least exists in the culture of Discworld, but it's really not an adequate foundation on which to base the standing of football at the beginning of this book. It suggests that Terry launched into the plot without much forward planning (despite the fact that the idea had been suggested to him years in advance.)
The football element wasn't the only part that felt underprepared for either. The protagonist, Mr. Nutt, for example, is a member of a race previously unmentioned in the series, which conveniently bestows him with exceptional abilities while making him the subject of severe prejudice, in a city that has become accustomed to members of most races introduced thus far, and granting him a Dark And Mysterious backstory. In a series that already has so much groundwork to draw on, this seems like a downright lazy way to design a character. And while other characters in the book were more tastefully conceived, they tied in poorly to the existing setting. Unseen Academicals introduces four new main characters, each with their own distinct subplots. There is barely enough space in the book to sufficiently develop them all as viewpoint characters and get the audience fully behind them while still adequately resolving their plots, and I don't think Terry quite managed it; the conclusions to the subplots felt abrupt and unsatisfying, save for the ones that weren't properly concluded at all.
Add to that a marked overreliance on running gags, in a series that used to stand out for the freshness and originality of its humor, and I couldn't help but get the feeling that Terry Pratchett doesn't really know what to DO with Discworld anymore. Following what I feel is something of a decline in the recent books, my impression is that Terry is at a loss regarding new and compelling ways to use his preexisting characters, but his dependence on introducing new ones is overcrowding the narrative. Maybe he has some really good books still left in him, but I'm becoming skeptical of his ability to work them out within his existing setting.