I'd like to start off saying that I'm a longtime fan of Sir Arthur Conan Doyle's Sherlock Holmes works, even before I watched the BBC adaption, the Hollywood films, or heard about the new CBS television show. A lot of drama has been going on in the BBC Sherlock fandom about how Elementary is a rip-off of their favourite show, and that it shouldn't be done. They may not like it because it messes with the Sherlock/John relationship people enjoy with Watson instead being a woman, or that it's an American version versus their beloved BBC show. However, I do not think that it is a rip-off. It's a similar concept, the idea of a modern Sherlock Holmes. It's interesting and and generally very cool.
Overall, both shows seem very different, from the acting to writing to the way they are filmed. (I am basing this off the Elementary previews that I have seen.) The only thing to do is wait until fall to see how similar or different these two shows actually are. I, for one, am excited to see how this new show will unfold. You cannot officially judge the validity of this interpretation without actually watching it. After all, any Sherlock Holmes is pretty awesome. It would have been interesting, though, to have Sherlock as a woman as well.
You are allowed to like both - you can be a BBC Sherlock fan and still want to watch Elementary. It won't make you any more or less of a fan. At the very least try and warch it to see, it won't hurt.
Elementary fall preview link: (x)