Okay, I was hoping someone would expound....so, I'll mention the biggie that I keep coming back to.

Canon has Severus Snape listedf as having "uneven, yellow-ish teeth" (Prisoner Azakaban 14), I think.

And, Alan Rickman, definitely does not have Yellow teeth in the movies. So, I don't think 'yellow' teeth would be an image breaker for me...LOL....but, some of the physical description of Severus Snape, does seem to be actually portrayed by Alan Rickman.

Anyone else have an opinion?

Snape gazed for a moment at Dumbledore, and there was revulsion and hatred etched in the harsh lines of his face.
'Severus ... please ..."
Snape raised his wand and pointed it directly at Dumbledore. 'Avada Kedavra!' (Half Blood Prince 27)

Now, it wasn't quite hatred and revusion that I saw or heard in Severus' voice on the movies....

In the movies, since they there they can show the emotions you only read about in the books, Alan added many facial expressions, mannerisms and unique "tics" to his behavior to give a visual idea of the character. His voice specially played a huge role in that. I tended to "hear" Snape's voice as one un-changing, nasty tone in the books. Except when he actually BELLOWS in both Prisoner of Azkaban and when called a coward. And speaking of that, the line "DON'T CALL ME COWARD!" was one I was disappointed not to hear in the movie(as well as him running away from Buckbeak!). I really wanted to -see- Snape loosing control like he did in the books. Not even when Harry intruded into his mind did he raise his voice. He kept it low and menacing. THAT is what Alan added to him different from the books. He was dark, brooding, mysterious and most of all a constant feeling of threat and menace. Whereas, in the books, he was just nasty and bitter.

I also loved the physical violence of him smacking the boys around and yet keep a calm face while at it. XD Nice little surprise from the books.

The part where he kills Dumbledore show him actually being remorseful and sad by it, the same goes when the Muggle Studies teacher is killed over the table in DH1. I didn't like Dumbledore's death much in the movie, but mostly because of Dumbledore's actor not sounding as pained as I imagined in the books, so it took away from the general effect of him begging Snape. Alan, of course, always knew about Snape's love for Lily and so knew the real character Snape was, but in the books nobody knew so the image that Rowling wanted to give was very different. Alan wanted to hint him having a softer side from early on.

When he's dying in the books. He's still cold and unfeeling. "Look. At. Me." was 'hear' in a clipped and terse way in my head.
But Alan, comes and delivers that scene with all the emotion you've never even thought Snape could show! Have him crying, grimacing in both pain and grief and actually -begging- Harry to take his memories. And the his softly and gentle "Look at me..." with the most perfect extra line of "You've got your mother's eyes..." that just made everyone who wasn't sniffling already start to do so.

And of course, last but not least. The scene that's exclusive from movie only. Snape hugging Lily;s death body to himself and crying over her. So those of us holding back the original sniffles started outright sobbing.

Couldn't have been played better!

Ok, ramble off!

I read the first book 12 years ago, and while I enjoyed the portrayal of Professor Snape, he wasn't a favorite character at that time.

Then 2 years ago I started watching the movies in earnest, and Alan Rickman's Snape exuded a sexuality that I didn't feel the book Snape had. I also had no idea who Alan Rickman was, but it turns out I had seen him in a couple other movies.

So that's really the big difference for me, and I've been obsessing since.

And nearly 24 hours after, I realize, duh, you're not going to have a really sexy character in what is, essentially, a kids' book. I don't know where my brain is sometimes.

I know. I just re-read the series again....now, after re-reading the series and starting to watch the movies, I know I have always had a fascination with Severus Snape.
But, the fascination with his sensuality is because, not only is there excellent fanfic out there, but, Alan Rickman as Severus Snape....sex on legs and a voice of silky chocolate.

Great description. Sex and chocolate--it doesn't get any better.