Because the general story of Dracula is so well known, it's easy to think that you'll know all of what's going to happen when you read the original by Bram Stoker. In fact, much of what is in the book is far more pschologically threatening than in any of the gore-fest films we've all seen. Stoker's Dracula is genuinely, breath-takingly menacing... and beyond redemption.
With Dracula you get well drawn characters relating their ghastly experiences, and you're not spoon-fed the narrative -- you have to join some of the dots yourself. There is a dark, sensual overtone to much of the novel (which puts many modern authors, who turn their books into total shag-fests, completely in the shade!), and a complete horror when Dracula is fully revealed.
But there are some downsides. The novel bogs down in the mid-section. The language is of its time -- so it takes careful reading if you're used to modern horror gallop-along novels. And much of the fear and loathing develops in the mind of the reader, not from over-wrought narrative.
So to get the most from Dracula you need to take your time reading it, and put some effort in.
If you prefer your thrills to be a little easier to access then I'd recommend Stephen King's 'Salem's Lot', or watch the film with Gary Oldman. They're not as pure as the original, but they do justice to the concept.
I first read Dracula when I was 14 or so, and it's just as scary now that I'm 40!