Dracula is a great novel. One of the things that makes it so great is that it was written in the golden period of English adventure/thriller/mystery literature, which gave rise to great writers such as Conan Doyle, R.L. Stevenson, and H. Rider Haggard.
The thing about Dracula is that it's a hard book to read. The main plot develops VERY slowly, and the idea of writing it thorough diaries seems quite strange at first, until you reach the point where you finally see the connection between them; And that point is around 150 pages into the story, which is quite tiresome for the (modern?) reader.
The thing I found most frustrating is that the first part of the book (Jonathan Harker's diary) is written fantastically. It's weird, quite creepy, the character of Count Dracula is described in a magnificent manner, and you can really feel Jonathan's fear as he realizes that he's trapped in Dracula's castle.
But then the story switches to Lucy and Mina for, like, a hundred pages, and I want to yell "what the hell, Bram? Don't give me this romantic bullshit, I wanna know what happened to Jonathan!"
Until you realize the connection between the various characters, you're already halfway into the book. Until that point, the book is confusing and inconsistent. When you reach the main plot, it really gets much more interesting, but you're still wondering, why such a long introduction? Of course this is intentional and important to create tension, but if you don't consider that the book was written a hundred years ago, when readers liked that kind of tension in literature, you really get tired on reading it.
Well, it all sounds like criticism of the novel, but I must say I really like it. It has some great quotes and I like the structure of it since it is so original. One of my favorite quotes is Dracula's shameless scorn of the Russian and Austrian royal dynasties:
Ah, young sir, the Szekelys, and the Dracula as their heart's blood, their brains, and their swords, can boast a record that mushroom growths like the Hapsburgs and the Romanoffs can never reach.