I don't normally write reviews, but I was moved to do so in this case after reading some of the earlier comments. In short, there's nothing at all wrong with this book except that it isn't Red Dwarf. But, you know, we have to accept the fact that nothing else will ever be RD, and move on. A suitable period of mourning has elapsed, I think.
Although Incompetence has a plot, of sorts, it isn't really that important. And maybe the characters are a bit like cardboard cutouts, but that isn't important either. Incompetence is really a vehicle for the author to make jokes about situations that piss him off. Now, if you can identify with these situations, you'll find the book funny. If you can't, you won't. No particular life experience was necessary to be able to appreciate RD. You may, or may not, have enjoyed its particular brand of lavatory humour and insults; but if you didn't, it probably wasn't because you don't have sufficient life skills. But Incomptence only makes sense, I think, if you have a particular mind-set, and have seen a bit of the world. For example, if you don't understand why the idea of a caterer being compelled to employ a waiter with Tourette's syndrome is funny, it won't help if someone explains it to you. Either you get it or you don't.
For my part, I started laughing from the first paragraph, and carried on laughing until the last page. In places I laughed so hard I thought I'd swallow my own eyeballs. At the same time, I can imagine a bunch of RD fans scratching their heads, and complaining that there's only one fart joke in the whole book.
In summary, the humour in this book is more like that in Dilbert than in Red Dwarf. Like Dilbert, the plot and the characters are sketchy. Also, like Dilbert, if you don't understand it, it's because it's about you. :)