I don't know what I would pick out of all the books I've ever read, but I think out of the ones I've read recently (since the beginning of the year), I would have to say it was David Drake's Lord of the Isles. It was either the most intriguing or the most confusing plot I've tried to unravel lately. It had an ensemble cast of characters, and it was clear they all had a part in what was happening, but very early into the story, everyone scattered in different directions. It was unclear for much of the book how, or even if, they were going to get back together and work things out. Add to that the sorceress tossed back in time by a magical maelstrom, a young man from a small village who channeled a king, and the young woman possessed by a vengeful demon and the plot, well, thickened.
I have to say that this was not the best book I've read this year. It fell flat in several ways for me. A few of the characters just didn't resonate well, and the one I really liked got killed. It was a good death, and fit him and the story, but still that lost that point of interest. I kept reading until the end to see how all the plot convolutions were going to work out, so I guess that puts this one at a pretty intriguing plot.