There were a lot of books I read or fast-read and I did not care that much for, but in many instances they were books that came with little expectations (middling debut fantasies like Spellwright, Conqueror's Shadow and the like), were sequels to series debuts that I was surprised I enjoyed a lot, so the expectations reversed to the mean so to speak (Prospero in Hell, All That Lives Must Die, Thirteen Years Later, Freedom) or were books where the series weight or lack of caught up with them (Echo, Deceiver, The Hypnotist) as I expected to sooner or later, so I was not that surprised.
The above on the other hand were almost all potential candidates for top-ten novels of mine based on previous experience with the author's work, content, vibe or hype ("the best debut" since, well you know the spiel) and they all did not work that well for me though in degrees, since despite all I still enjoyed Michael Flynn's Up Jim River but far from the superb The January Dancer since the combination of archaic language and Vancian travelogue on strange worlds degenerated into farce quite a few times, Alastair Reynolds' Terminal World is still better than most sf out there despite being essentially a combination of two books without almost any relation between them - each could have been magnificent on its own but together they are a jumble - and Adam Roberts is still mostly entertaining despite committing the sin he railed against Greg Egan in his (in)famous review of Incandescence, but with lit-grad musings that would be quite appropriate in a discussion after a drink or two and which otherwise take down New Model Army badly, rather than with the "too much science" of Incandescence...
Both Absorption and The Orphaned Worlds suffer from too much ambition in too little pages, trying to be epics with tons of threads in 3-400 pages and both fail as incoherent, though I plan to read the sequel to Absorption hoping that there will be a better balance.
Engineman wears its age badly and is annoyingly parochial to boot (the 2010 edition is a revised and expanded version of the 1990's original), while The Dervish House's world building is a tourist postcard one showing the author's lack of understanding of Turkish culture.
The Horns of Ruin is a comic book novelization with a ridiculous straight-faced earnestness and lacking the humor that make such palatable even in small doses for me, while C is the epitome of pretentious drivel that made me eschew a lot of what passes for "literary" for so long - though once in a while it's good to be reminded why sff is still the most interesting and relevant literature of our age and C is a good such reminder.
The Quantum Thief is a reasonably entertaining debut, though it's only slightly more interesting and "serious" than the usual Scalzi/Sawyer B-grade of sf and it lacks the panache of some such like Old Man's War being a far cry from the hype pumped relentlessly on the web about it. Without said hype I actually may have enjoyed it more and I definitely plan to read the next book in the series since there is potential there. On the other hand 20 years of heavy sf reading accustomed me with the discarded remains of "debut/series of the age" hype (anyone remembers the Plenty books of the 90's or more recently the Will McCarthy novels of the 00's, both series having the same vibes for me as this one) so only the future will tell where this series will go.
The Dream of Perpetual Motion is a book I *really* wanted to like - its subject seemed tailor made for my taste; sadly the author' style just did not work out for me and the novel read flat and lifeless, while Tome of the Undergates was almost so bad as to be funny at the level of the North Korean movies of my childhood that were unintentionally quite hilarious; not there though, the all-caps words and philosophical discussions about potty habits do not reach the epic level of the farmer who shook hands with Kim Il-sung some decades in the past and the hand in question became an object of worship in the village, not ever to be washed so not to dispel the Great Leader's touch, so the author has a way to go until he reaches those heights...