This is a good question Ropie. It actually got me thinking quite hard about some of the books I've read and why they've stayed with me. I consulted my list of books read (yes, I have a list, which I realise sounds a bit eccentric...), and was quite surprised by how much of the SF I've read in the last few years has been pre-2000.
Thinking on this I suppose it is down to there still being a great deal of "older" SF that I want to read and that appeals to me more than some newer works. In ten years time I'll probably be catching up on all my 2000 reading!
Getting back to the OP, I've got four that I think are about equal for me. Altered Carbon by Richard Morgan I really enjoyed, and I found the whole story engaging, with some memorable scenes. Scalzi's Old Man's War was a great read, and felt his approach to interstellar war was interesting and thought provoking. Neal Asher's The Line of Polity was a very fun read with plenty of action with some good scenes for me.
Lastly, and perhaps, PERHAPS shading the rest, is Peter F. Hamilton's Fallen Dragon. Hamilton's Night's Dawn trilogy was my first real introduction into the genre and it remains one of my all time favourite series. For me Fallen Dragon encapsulated a lot of that 'epicness' and was a great space opera in its own right that had great characters and plot.
(Oh, I'll also approve of Use of Weapons as one of my all-time greats. Between that and Left Hand of Darkness for me).
