Amis must be doing something right - I managed to read this book to the end, and found I just about continued to care about some of the characters, even the relatively minor ones.
I found myself laughing out loud at the "one-liners" in the early part of the book, but thereafter the wit faded. The main "Italian holiday" section had plenty of potential for amusement, intrigue and sex, and yet Amis only partially delivers - although there's obviously some clever irony in the fact that the reader (and the main protagonist Keith) is never quite satisfied, and never reaches the spectacular sex scene - at least, not in the way we (and Keith) imagine it.
Where the novel mainly falls down, however, is in its spectacular pretentiousness. Keith's early witticisms eventually turn into dull showing off (on his and Amis's part) as he ploughs his way through the English novel, author by author (presumably for his studies). And Amis's attempts to explore his (Keith's) emotional and sexual life eventually become so convoluted, alienating and unengaging that you wonder why you ever warmed to him as a character. I started off by recognizing something of myself and my life in the characters, but that feeling soon dissipated.
Of course, all the pretentiousness may be ironic, knowing, arch, or whatever - but ultimately you end up not caring. Sometimes an author pulls the rug from under you so many times the effect becomes tarnished.
The structure, too, eventually falls flat, as if Amis were trying to cram too much detail into the series of truncated chapters at the end, having produced an overlong first section.
What the book did do, however, in addition to amusing me, was challenge me and take me out of my comfort zone. Those are the reasons why you should read it.