''It was a very strange, schizophrenic season,'' admits creator Joss Whedon in one of Buffy The Vampire Slayer: The Complete Fourth Season's featurettes. He's got that right. The fourth year of the series, which follows the Scoobies to college, yields some of the show's smartest, most daring episodes (the all-but-silent ''Hush'' proves Whedon's narrative gift goes beyond sharp dialogue) and showcases the dramatic chops of the cast. (Speaking of which, a behind-the-scenes short on James Marsters' platinum-haired Spike livens up the otherwise not-so-special special features.) The overall story arc, involving a government op called ''The Initiative,'' is too entrenched in hard science to ascend into the magical, epic Buffydrome we know and love. And bland, corn-fed Riley (Marc Blucas) as a replacement for the Slayer's ex-b.f. Angel (David Boreanaz, who tantalizes us with two brief appearances)? Puh-leeze. We'll take our love interests like our conflicts: dark and mystical, thanks.