So you're saying HotDQ is more sandbox than linear adventure? That if the players decide to off in an unanticipated (but not illogical) direction, the book supports you in handling that?
I wouldn't say it's very sandboxy, no. But linear does not always equal railroad, or if you want to call it a railroad just because it's linear, than I would argue that railroad doesn't have to always be bad way to play the game. Don't get me wrong, I want player decisions to matter, and those who are complaining that the only BIG choice the players have in HotDQ is to participate in the adventure or don't participate in the adventure.
I see plenty of little choices. The adventure doesn't spell-out exactly what to do if the players make a medium-sized choice that's off-script, but it gives suggestions on ways to roll with most reasonable possibilities. Basically, as long as the players buy into the story (which shouldn't be hard to do if the DM doesn't spend time treating it like it's stupid - it's not if you don't play it that way.) they will probably be happy to go along with all the big "railroad" moments even if the adventure hadn't been written that way.
Most players I know make characters that would actually want to go on an adventure. You know, adventurers. So they're generally pretty quick to jump on any hook that seems reasonable.
As far as some of the complaints like "The dragon doesn't kill you for some stupid reason" goes, I think it's pretty simple (and pretty much spelled-out): It never wanted to be there in the first place, thinks the whole thing is beneath it, and has probably been flying around for hours by the time you "confront" it. Why bother to psychotically murder you when it could just as easily head home?
The same argument was made about the half-dragon not killing you. He stabs you while you're down. Does he really need to check your pulse and stab you again? Does he have some way to know you have one death-save remaining? He leaves you for dead on the battlefield having defeated you in front of a crowd. It's the most likely way for it to go, but other possibilities are mentioned.
Ah, whatever. I'll have a better understanding of it after I run it.
Hey, I didn't notice - was the whole OP based on reading it or on running it?