To agree with others, the character of Walter Bishop is extremely entertaining. He's not believable. The show can't seem to make up its mind about how mentally ill Walter is. Even worse, the producers seem to think that a mentally ill scientist is a particularly well qualified one, instead of one who can't do science because he's sick.
One character doesn't make a show, however. Peter Bishop is slowly being modified to a character hanging around because he wants a relationship with his father. But his original motive (horny for Olivia Dunham) still lingers, and the show's plots are all skewed because there's no real reason for him to even be there, much less be Olivia's partner/boy friend. The producers seem to think that Peter's militant ignorance makes him cool, instead of realizing it just makes his presence even more inexplicable.
The so-called mytharc is only interesting in respect to the Walter/Peter dynamic.
The less said about Olivia the better. Anna Torv is very attractive so maybe you won't want to throw things at the tv when her character's on.
My recommendation is do not, do not, buy
this until it's marked down to $6 for a season set at Big Lots.