As a general rule, it's more dangerous to follow success than failure. If the new series is about average in quality (and most new series are, that's what "average" means), it will suffer from comparison to Whedon's series. Fans will think it's kinda good, but not as good as the "real" Buffy.
I'm curious to see what they do about cell phones, which were not yet ubiquitous in 1997.
After the series finale, there were dozens of slayers running around. Following one of them seems better than rehashing Buffy's story. Supposedly there were other Hellmouths. It could work.