When I moved to Minneapolis, my soon-to-be-former colleagues gave me a lovely going away party. My favorite gift was a book (big surprise); its title: How To Be a Villain.
This book is hilarious. Replete with quizzes, name-building exercises, suggestions of what type of lair would best suit you as a villain, it keep you laughing from start to finish.
It's also a great commentary on the type of villains who work well in a Bond film, but won't hook your readers in a meaningful way. These villain are caricatures - they may have nasty-looking minions and terrifyingly giant electro-ray guns, but at the end of the day we know they won't win. We can't take them seriously.
Villains have to be seductive - and I don't mean in a romantic way. Evil focuses on the accumulation and retention of power for its own gains. It promises dreams fulfilled, goals achieved but with a price.
In order for a villain to be compelling, the reader has to understand what kind of allure the 'dark side' holds, even for our most pure-hearted MCs. The thought that our hero/heroine might indeed cross over at any point should be a constant, nagging worry.
A good example: Voldemort. Now you might be thinking - how could you get more evil than Voldemort? I agree. Voldemort is a super-duper big bad. But if you remember a key moment in Harry Potter and the Sorcerer's Stone, Voldemort is able to tempt even Harry - offering him power, the promise of parents restored. Harry resists, but the temptation of dark powers is clear. The reason Death Eaters exist stems from their desire to share in the power that Voldemort wields, to rule over others even if by wielding terror and pain.
What I think may be the best example of evil's true nature to this day is Oscar Wilde's Picture of Dorian Gray. This story illuminates the double-edged sword of villainy. It has to allure, compel, always beckon. The risk of the hero or heroine falling into temptation must be ever-present, and his or her ability to overcome said temptation is as much of a triumph as the longest chase/explosive fight scene in any book.
And once that temptation is overcome, when evil has lost its chance at winning by seduction - that's when the facade of beauty crumbles away to reveal the villain for what he or she really is: EVIL.
Dorian Gray offers close to a literal exposition of such a moment. And hey, what do you know, they're remaking the movie.
Cannot wait (sidenote: if I could pick, Ben Barnes would play my character, Ren, in a film adaptation of Nightshade. Sigh.)