I'm a new fan, I love it. Was a perfect amount of dark for me when it did get dark, in addition to being pretty funny. Plus with the shorter amount of episodes, it seems alot tighter, less fluff. The US version is just way too emo and melodramatic, but I'll still check it out when it returns.
The overall plot is similar, but there are some major differences between the two worlds. For example, the BBC version vamps didn't appear to have any powers. No superspeed, no super strength, just the bloodlust, the immortality and the ability to be in sunlight, which the US version also shares. The main vamp guys are portrayed differently as well. In Buffy terms, Mitchell's seems more akin to Spike, while Aiden seems more akin to Angel. There are some major differences between Annie the ghost and Sally the ghost that are noticeable off the bat. George is less of a pansy compared to Josh. He actually is a bit of a dick at times. All in all great show!
To each their own Temis, but I think you should give it (BBC version) a shot, sometime.
And if you're not gonna do it for me then do it for the kids. The kids, Temis, The Kids!