Personally, I think Tyson is the BEST replacement available for Carl. I agree, whole heartedly, that no one could ever replace him, but at least Neil knew him, learned from him, and admired him.
The thing that I like most about the new Cosmos is that Tyson is so completely genuine. Like Carl, when he talks about the age of the universe, the number of stars in the sky, or the scientific method itself - he feels it. Through and through. And yeah, maybe he's just acting, but it's a damned convincing act, if so.
The joy of knowledge is contagious. When someone truly embraces learning - not WHAT they learn, but the actual process of learning - then the people around them can't really help but get caught up in the enthusiasm.
And we so desperately need some enthusiasm towards science...