I have to admit, I'm kind of schizophrenic when it comes to dialogue in games. I can fully appreciate locking in the player during dialogue--if the player is given dialogue options. Outside of RPGs, though, dialogue is almost always glorified cutscene (think HL2). At least dialogue trees give you SOME choice (even if in most cases it's only the illusion of choice). Most of the time, though, it's far better to show the player something rather than tell them, and then, it's preferable to let the player do it rather than show it (or if it's literally impossible for the player to do, let the player discover it on his own).