The most overrated book:
Everything by K.A. Mitchell
Chicklit/fanfic-style writing re-written into m/m with some of the most repetitive, unsexy, unerotic, surplus and unnecessary sex scenes taken from porn flicks ever.
More overrated books...
"A Long, Long Way" by Sebastian Barry
Factually wrong more often than right, picking the wrong causes, terribly purple and overblown prose.
"Fight Club" by Chuck Palahniuk, Martin's "A Song of Ice and Fire"-series, Bujold's Vorkosigan Saga, the Twilight-series and its tail-end Fifty Shades of Grey-series, quite a few of Georgette Heyer's books (yeah, the Regency brigade will flame me to cinders now :P )