I'm a 27-year old guy, and I read Twilight - along with my sisters and mother - and absolutely enjoyed it. Although the novels are aimed at teen girls, they also appeal to a broader range of readers. Of course, just like almost anything else, they're not going to appeal to everyone. Regarding the movie and its chances of success, I actually haven't personally heard of any overwhelmingly negative reactions to the film thus far; most of what I've heard has been positive, especially since the filmmakers have gone on record as wanting to strive to be as close to the novel as possible.
As to whether or not vampires have become the 'next big thing' in pop culture, vampires have always occupied a niche in pop culture, but the overall popularity of vampire-related material seems to fluctuate in cycles.
Indeed as an 18-year old guy I'm not exactly in Twilight's target audiance but I loved all four books in the series (the first one especially). The original novel asn't written to a teen girl audiance but that's who mostly flocked to it.
As for the movie I am cautiously looking forward to it. I really didn't picture Edward or Bella as lookng or sounding anything like the actors who are playing them do. Honestly I think Twilight is one of those things that would be best left to the books since a lot of the wonder (impossibly beautiful people with perfect voices) is hard to portray. I definately will see it though and probably in theaters.