To call 'Grand Horizons' one of the brightest shows to hit Broadway in years is not to tout its intelligence, which flickers. Rather, I mean that it is blindingly lit, no doubt in deference to the theatrical wisdom that defines comedy as what dies in the dark. And, boy, does 'Grand Horizons' want to sell itself as comedy. Not witty comedy with its verbal arabesques, nor intellectual comedy with its Paris Review name-checks, nor meta-comedy with its scrambled plotlines - but the vanilla kind that once dominated commercial theater. It's not entirely meant as praise to say that this Second Stage production is a big-laugh, blue-joke, bourgeois lark of the type Neil Simon mastered until the times mastered him and the genre petered out. There's a reason it did, and perhaps what the playwright Bess Wohl is attempting in 'Grand Horizons,' which opened on Thursday at the Helen Hayes Theater, is a last-ditch act of reclamation: a boulevard comedy for a cul-de-sac age.