And if you haven't seen it... yeah, you aren't going to understand all that much of this, since most of it is about how The Scene That Ought To Get Rickman An Oscar compares to the book version.
First up, kudos to Alan Rickman for managing what neither J.K. Rowling or Jim Dale ever did to me: making the Potter Puppet Pals skit "Bothering Snape" stop being funny to me anymore.
Second, I liked the way some of the changes from the books were foreshadowed in earlier movies. The horcrux sensing wouldn't have worked if there hadn't been the incident with the ring in HBP and the discussion with Ron in DH1.
Third, Snape v. McGonagall rocked. It wasn't the same as the book, but the way the Carrows are defeated is quite satisfying. And there is still a Snape-sized hole in the window even with the location switch.
Fourth, I actually liked a lot of the changes to That One Scene from "The Elder Wand". I thought I'd hate the location change when I first heard about it, but they used the glass effectively, it let Hermione and Ron both see what was going on instead of relying on Harry's connection with Voldemort to show what was going on, it meant Snape wasn't lying flat on the ground when the Trio walked in, and I'd honestly wondered how the book version could be filmed without getting the entire film automatically rated R. The initial spell hit, with the sudden spread of blood seeping through the white collar, worked a lot better visually than the book version would have, and the change of location let the Nagini bits be heard and vaguely seen rather than be completely on screen.
I hadn't heard any rumors about the death scene itself. The more I think about it, I really like the changes. Referencing back to my first point, Rickman's Snape here is someone who has finally had the facade of personal control completely collapse. Sure, the book has the 'trembling foot' description, but that's an uncontrollable physical shock reaction, NOT a characterization point. In the book, he still has the physical control to cover his wound with his own hand and also grab Harry's shirt firmly enough that Harry cannot leave the room until after he is dead (and the fact he has the strength to do it until the death slump is one of my major gripes about how the book handles the scene). In the movie, he doesn't even try to cover his own wound. Other than a few gestures towards the memory tears with one hand so that Harry understands what he's talking about, Snape doesn't move anything but his head, eyes, and mouth. It's Harry who covers the wound, and it's completely his own choice to stick around until Snape stops moving rather than immediately running off with the vial toward the pensieve.
And Snape gets an extra last line, completing the set of people close to Lily who tell Harry he has his mother's eyes. Given the way Harry already seems sick of hearing it when Sirius and Lupin both tell him that in the Prisoner Of Azkaban movie, it fits like it would not have in the book.
I'll admit to not crying, after having brought extra tissues with me thinking that I would, but I think most of that was the absolute shock at the emotion Rickman was putting into the scene. I'll probably cry the next time I see it, the same as I didn't actually have an emotional reaction to the scene in the book until the third reading (which would be the second I'm-reading-slow-enough-to-understand-what-is-going-on reading, given that I didn't realize Snape was gone until halfway through The Prince's Tale flashback my first reading).
The group I watched it with Monday must have mostly been either book fans or repeat watchers, because people started reaching for pockets and purses when Voldemort told Lucius to bring Snape to him.
One thing I did not like at all: The "I have spied for you, and lied for you, even put myself in mortal danger for you" line was gone, and it really cut the 'this is just how much Snape actually did for Harry's safety and Lily's memory' aspect of The Prince's Tale. I hope there's an extended version when the DVD comes out, because that cut really changed the memory sequence.
Another thing I didn't like: they should have stuck Snape's Worst Memory in properly seeing as how there's no mention in the entire movie series as it stands of exactly why Snape and Lily's friendship fell apart at all.
And now I really really can't wait for the DVD release so I can go frame by frame and line by line on that entire sequence.