Spoiler free! This review only contains background information and general information.
I was skeptical of this show at first, because I was told that it is a teen drama. Since I am 28, this did not appeal to me, until a 32 year old friend of mine showed me some clips from the show. I immediately had to watch it. While the first episode did seem a bit juvenile, the show quickly started to transition, and I would not hesitate to say now that this show is made for adults. While there are 22 episodes, one could easily sit down and watch each 45 minute episode back-to-back on a lazy Saturday... it would be worth the sleep deprivation. The Vampire Diaries has quickly become my favorite show (in case it helps you, my other favorite shows are Dexter, True Blood, Buffy, Veronica Mars, Bones...).
So which audience is this show for? The CW targets the show towards 18-34 year old women. Yes, you read that right; this is not supposed to be a teen show (although they can watch it and enjoy it).
The show centers around a small town (yes, the town is one of the main characters) called Mystic Falls. About 145 years ago, vampires existed in this town, but then the townspeople who knew about their existence torched them. Some escaped and moved to other places. Most of the current townspeople don't know that vampires exist.
I think the actor who shines the most in his role is Paul Wesley who plays Stefan Salvatore, the eternal 17 year old vampire. Stefan has returned to Mystic Falls because of a teenage human named Elena who looks identical to an evil vampire named Katherine he loved, who was killed 145 years ago. Not to worry, the actor is 28 in real life, and he doesn't look like a teenager, so you won't have to worry about feeling like a cougar. Stefan is a lot like Angel from Buffy, because he broods and hates himself because of what he is; he refuses to drink human blood. He also has secrets and regrets, which he thinks about daily. You could think of him as the vampire with a soul if you wanted. Although he plays the sweet vampire, you can still sense (actually it will come out temporarily) that he has a dark side and could possibly be a bad boy if he wanted to. His acting prowess shows even more in season 2 when he gets over his issues and embraces his true nature.
Ian Somerhalder plays Damon Salvatore who is Stefan's older vampire brother. This is the true bad boy. Well, the bad boy with a heart. Not a heart of gold, but he does have some humanity. Damon is the prime reason why some people I know watch this show. Actually, it's hard to tell if it's because of Damon or Somerhalder himself. Damon has come back to Mystic Falls for a couple reasons: to make Stefan's life hell and another reason which will be revealed later in the show. You see, Damon was also in love with Katherine and he can't live with the fact that Katherine turned Stefan into a vampire, since he thought that Katherine only loved him and wanted to share eternity with only him.
Elena, played by Nina Dobrev (of Degrassi fame), is a 17 year old who has just lost her parents in a car accident. She feels dead inside, but then she meets Stefan and he fills the void. No, this isn't going to be just like Twilight (the Vampire Diaries is a unique story--it has a bite). Elena might not only end up with one suitor, because just like Katherine, she has more than one admirer. The viewer has to wonder if there is foreshadowing involved when Elena is warned that as long as she has a Salvatore brother on each arm, she's doomed. This love triangle is very subtle the first season, but it's impossible to miss. Again, another prime reason why some viewers tune in.
The secondary characters are just as interesting and fun to watch, so while there are many story lines, none of them are boring.
Watch this show for the great storytelling, Paul Wesley's acting, the eye candy, the love triangle, or for your favorite character (because you will have at least one and there is great character development).