Tom Hiddleston and Tilda Swinton were marvelous as the leads. They are presented as aging vampires, trying to seek their place in a modern world. Though we're never given the inception information (i.e., how they became vampires), it seems they've been creatures of the night for many, many centuries.
At first I was a bit miffed at the movie's casual adoption of ideas from other vampire movies and novels. But they ran with it in such an entertaining way, I forgave them entirely.
Imagine living for a thousand years. One of the things brought out in the movie is that you'd know many things. These two vampires are experts in so many areas, it makes your head whirl. And they seem to have senses beyond ours, though these are not explained to us. They're just very perceptive and seem to know everything.
I won't ruin the movie by going any further into it. It's definitely worth watching if you're a fan of either horror or great movies. The music, the cinematography, the script -- all are engrossing and so damn stylish. This movie is art.
I suggest watching it with captions turned on. The script is that delicious, and you might miss a few words. Enjoy. PS: Here's the trailer.