Blair Witch Project is interesting for two reasons:

1. It did the early ARG publicity thing by planting stories online before the movie
2. It kicked off the found-footage horror trend that continues to this day. It wasn't the first but it is better than most. Its commitment to trying to present itself as if it were completely true is more pure than most later movies that are presented as partial or full dramatizations, or are too silly to be convincing, use special effects, etc.

It is not a perfect movie by any means and the rewatchability is zero but it is memorable and historically important.