The first season is highly regarded.

At the time, the second season wasn't as well received, but fans of the show still enjoyed watching the show, mostly because there was nothing like it on television.

As to why the show is legendary, Twin Peaks is a deconstruction of traditional television shows and a comment on America.

The stuff you think is irrelevant is in fact relevant.

Having said that, the second season is flawed and simply not as good as the first season.