My Review of Harry Potter and the Half Blood Prince.

[Carol]

Carol earlier:
> > I realize that they omitted his sending the Order to the MoM in OoP, which I think is an unfortunate oversight.)

Eggplant: 
> I don't see what's so important about having that in the OoP movie, it tells us nothing about Snape's character. <snip>

Carol again:
Nothing? It tells us (and should tell Harry) that Snape is a loyal Order member who risked discovery by LV in sending the other Order members to save Harry and friends. Can you imagine what LV would do to Snape if he discovered that he'd alerted Sirius and company to Harry's danger? Snape thwarted his plan. Harry was just about to hand the Prophecy Orb over to Lucius Malfoy (in both the book and the film) when the Order showed up.

And not revealing that Snape sent them leaves moviegoers with no explanation of how the Order members knew that Harry and his friends were in danger. It's a plot hole.

Carol, noting that Snape did *not* think that the MoM plan was canceled (he informed the Order that Harry had not returned from the forest, sending them to the MoM, but went into the forest to search for Harry and Hermione just in case something else had happened