I agree with all of the above, but especially about the twist endings. There's nothing worse than illogical plot twists thrown in just to get a reaction. I'm one of those people who tend to figure out what's going on pretty early in a story, and I don't mind being surprised or wrong as long as it makes sense. If I'm wrong simply because the author thought, "Gee, this isn't subtle enough. I know! I'll completely throw everything I've written out the window to do this!"
On that note, foreshadowing can be extremely subtle and still work.
Spoilers for Brandon Sanderson's Mistborn trilogy follow. Don't read if you haven't read the books - trust me.
[spoiler]In the first book, Vin's earring didn't seem to be a big deal, but then it comes out while she's fighting the Lord Ruler and after that she can use the mist as an allomantic substitute. In the second, it gets ripped out again and she's able to use the mist again. She doesn't understand what's going on with the mist or if it's something unique to her (it is), and she doesn't know what causes/prevents her from using the mist. Not until nearly the end of the third book is it revealed that the earring acts as a hemalurgic spike in her ear, thus repelling the mist (as they're opposing forces - one of Ruin and one of Preservation). In the first and second books, the earring coming out occupies maybe two sentences apiece, and hemalurgy isn't explained until the beginning of the third book.
Theoretically, one could connect these dots as soon as hemalurgy is explained, but it's so subtle that that doesn't normally happen. In fact, everyone I know that has read the entire series was not able to guess this particular twist.
My point, in short: it's an absolutely brilliantly well done plot twist that didn't undermine anything in the series. Sanderson took the care to show from the beginning what was going on - even if the reader doesn't connect the dots until Vin does at the end.[/spoiler]
Conclusion: If you want well done plot twists, read anything of Brandon Sanderson's. He doesn't always use them, but when he does, it's genius.
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