I tried Consider Phlebas and can honestly say it was very weak. I started off OK and then quickly went downhill fast. I wouldn't bother with it.
I've read that one, actually, and had mixed feelings. But I've been told by many people that the rest are different and much better, so it's been on my list to try again for a while.
Aside, if you like John Ringo's Troy Rising, I'd recommend checking out Schlock Mercenary, a web comic that is set in the far future of the world of Troy Rising (Ringo read the web comic and was taken so wrote a story about how the first contact from the comic may have happened).
True, the radio series was the best adaption, but I liked the books too. It was the latest movie that I thought was uneven.
^That's just it, though -- the radio series was the one form of it that wasn't an adaptation, because that's where it originated.
Despite the man's real life politics, I really enjoyed the first Ender's Game, and the rest of the series is pretty good even if it goes in a totally different direction. Never did get round to the Shadow series. Forever War is brilliant, the sequel Forever Free does a similar thing. The thematic sequel Forever Peace explores the same ideas but in a slightly different universe. There's apparently a short story that explores the space between War and Free from a different character, but I literally just found out about it while I was looking up the names for the sequels. I've always meant to try the Honorverse by David Weber, but have never got round to it.
I am surprised no mentioned Dan Simmons sci-fi series Hyperion Cantos. It took me a while to get through the first book, Hyperion, but the payoff is considerable. Another book I only recently finished is Peter F. Hamilton's The Reality Dysfunction. It is the first novel in the - The Night's Dawn Trilogy. I have got the second book lying on a shelf. The first took quite an effort to read but it is excellent. As for other sci-fi epics. Dune is a dead giveaway and so is Alastair Reynolds Revelation Space. I especially enjoyed his standalone novel Chasm City.
^Chasm City is in the Revelation Space universe, as I recall. So it's not entirely a standalone, though it is one of the books that are apart from the main 4-novel sequence.
I am in the midst of Kim Stanley Robinson's Mars trilogy, and I can heartily recommend them! Red Mars was brilliant, and Green Mars is shaping up just as good so far.