Books that disappointed me for one reason or another - not quite living up to their hype, falling short of the author's other works, not as good as their prececessors, or books I simply disliked. You may see a lot of these books on other people's "Favorite" lists. Here's a contrary opinion - proportional to the book's popularity. In order from more recent releases to older books.
Geosynchron (Book Three of the Jump 225 Trilogy) by David Loius Edelman 5/10 I completely loved the mad infectious energy of the first book, "Infoquake," but with "MultiReal" and even more so with "Geosynchron," the story took a grim turn and felt more and more leaden and heavy to me. "MultiReal" still carried on the momentum of the first book, but I had difficulties getting through "Geosynchron" or caring at all what happened to these people.
This Is Not a Game by Walter Jon Williams 6/10 The weakest book by Walter Jon Williams that I've read so far.
The Name of the Wind (Kingkiller Chronicles, Day 1) by Patrick Rothfuss 7/10 Way overhyped, in my opinion. Engaging at time, annoying at others. Most people love the language, but I found the writing and pacing to be uneven. The scenes in the tavern framing the backflash story boring.
Old Man's War by John Scalzi 5.5/10 Scifi lite. Aside from the interesting premise (taking elderly people ready to die and giving them new bodies & lives as soldiers), completely unoriginal. The newly-resurrected characters might as well have been teenagers for their depth of thought and eloquence of conversation. The writing, while easy enough to read (no long words), is not very good; there are some truly atrocious phrases (hands down worst sex scene) and jokes. Plotwise, nothing you haven't read in Heinlein's "Starship Troopers," Haldeman's "Forever War," or Steakley's "Armor" - all far superior books to this one. Newcomers to science fiction who haven't read the works I just listed might find "Old Man's War" interesting or entertaining, but I found it to be devoid of value, literary or entertainment.
Glasshouse by Charles Stross. 3.5/10 My overall reaction to "Glasshouse" was Ugh. (Outrage at the Hugo nomination, but that's a different story) Meandering, dull, depressing, alternating some odd non-parody of our modern life with far-future infodumps that have nothing to do with the story. Again, Stross takes one interesting idea and buries it under a clunker of a story. To be fair, the writing's improved from his first novel, but I like this one even less, as his gender stereotyping left a bad taste in my mouth. L.Timmel Duchamp did a great review of it in Strange Horizons, capturing the essense of my reactions, but with in-depth analysis and brilliance (sidenote: *there* a scifi author to read). The promising beginning and the cool technology/far-future details were buried in an unclever, and at times simply wrong, parody of the 20th century lifestyle. I see no reason to read or recommend this book.
Blindsight by Peter Watts. 3/10 I found this book overall to be incomprehensible, nonsensical drivel. Barely original - like a bad, bad meld of Arthur C. Clarke's "Rendezvous with Rama" and Elizabeth Moon's "Speed of Light." Don't be fooled by a promising beginning. It doesn't get better. It gets worse, without any satisfying payoff.
The Chronoliths by Robert Charles Wilson. 6.5/10 This book is fairly well-liked, and I'm probabably in the minority being a bit let down by it. Interesting ideas: war monuments from the future arriving, but too short and not developed. Not enough scifi and explanations.
Factoring Humanity by Robert J. Sawyer. 6.5/10 Again, popular author, popular book. It just felt a little empty - too much focus on a nonsubstatial family drama. A scientist works to unravel the aliens' message, which will reveal something about the human race. Similar to Sagan's Contact.
Raft by Stephen Baxter. 7.5/10 This is actually pretty good, surprisingly entertaining hard sf. In a universe where gravity is hundred of times greater, humans toil to survive. This one's worth reading. Why on this list? Ah, it's Baxter's first novel. That explains a lot. He gets better, setting the bar pretty high for his own novels.
Armor by John Steakley. 7.5/10 This book was very highly recommended to me, and ranks as the favorite for a lot of people. In a take on Starship Troopers, humans battle insect-like aliens. The first half of the book is truly awesome and worthy of the hype, but the second half completely switches focus, storyline, and characters, and I got bored and stopped reading. Bummer.
Legacy by Greg Bear. 6/10 It's alright, not outstanding, and weaker than "Eon" or "Eternity." A man struggles to survive after being stranded on a strange planet where evolution took a different, non-Darwinian path.
Sundiver (The Uplift Saga, Book 1) by David Brin. 6.5/10 I read because I thought it was a prequel to "Startide Rising" - not so, this is a weaker book and not at all necessary. A solar expedition hopes to find the alien race that uplifted humans to sentience. Detective story.
Anvil of Stars by Greg Bear. 5/10 Although I usually like his works, this one left me lukewarm. Teenagers on a spaceship search for alients on a mission of revenge. I didn't like the yucky sex descriptions and didn't found it original or interesting enough.
A Paradigm of Earth by Candas Jane Dorsey It's profound, I'm sure, but slow-moving, and I'm not literate enough for it, or something.
Singularity Sky by Charles Stross. 5/10 This is his first novel, and the low star rating agrees with me. The Festival is a traveling civilization of aliens & information that loves to land on backwaters planets and hear their stories. However, the story lacked development and was ultimately dull. However, since Stross' consequent novels received better reviews, I'll give those a chance.
Nightfall by Isaac Asimov. 5.5/10 On a world with six suns, night only comes once in 3,000 years. Now's that time. Works better as a short story. As a novel - lacking.
Titan (NASA Trilogy, Book 2) by Stephen Baxter. 5/10 One of my favorite authors, just not with this novel. Before being disbanded, NASA wants to establish a research station on Titan (Jupiter's moon). Realistic, but plodding and unintesting.
Crossfire by Nancy Kress. 5/10 Average science fiction novel Kress's "Beggars in Spain" trilogy is quite good, but I probably won't seek out other books by this author. Unless you convince me otherwise!