I watched the 1st episode of The Vampire Diaries tonight, and here is my first impression:
Literally within the first 10 minutes of the show, there was murder and drugs. I thought "We're off to a good start", because Twilight has none of that. I read in an article that there's sex involved at some point too. Although Stefan and Elena do physically resemble Edward and Bella, their personalities already seem different, especially when comparing Elena to Bella.
I admit that as an adult, I felt a little embarrassed watching a show about high schoolers, but at least in Diaries the vampires actually look and behave more like vampires than their Twilight counterparts ( ie they have fangs and actually kill people). There were even some scary moments here and there! I'm particularly interested in Stefan's psychotic vampire brother Damon. I like that he has softer facial features than Stefan, and he seems charismatic, as a good villain should.
All in all, I was not disappointed in watching Vampire Diaries, because it successfully managed to combine traditional vampire viciousness with teen drama. I do not regret watching it one bit, and... I'm actually looking forward to more.