Gawd-Awful (spoilers)
Incompetent writing and uninteresting characters.
Old Man Spencer Fonda is a looney: first he drops a tree on his dear old dad, then burns down "the dream house" in a fit of pique. Plus he's not funny when he's sauced. Ralph Waite's Pa Walton completely skunks Fonda's Spencer in all departments, including Brains.
Dear old Grampa is merely an ornament, a fixture, with no discernable traits other than being Grampa. Not only that, he's as clueless as his alcoholic son. ANYONE who can be so distracted as to walk straight into a falling tree - walking for the better part of a minute in a straight line for about forty feet straight into disaster - is hardly a sympathetic character ... and because of this, the Great Spencer Family Funeral has very little emotional gravitas. "So, looks like the old guy bought it - huh, how 'bout that?"
Max Steiner's semi-"pop" score is effete, precious, self-conscious and obtrusive. Sure, Steiner was one of the "Greats" in movie scoring (the classic King Kong comes to mind) but his understanding of technique did not evolve with the times. Particularly annoying is his coy and cloying music for the extremely UNcute relationship between Clay-Boy and Slut-Girl, which brings us to:
The writing is insufficiently subtle to walk the line between Rural-Rustic-Lusty humor and Salacious, Winking, Sordid Barnyard flatulence. The entire movie showcases a "What If They Do It"/"Should They Do It"/"Will They Do It" - and finally, "Look, They're Really Doing It" progression of ... "erotic suspense".
But it's not suspense at all. This film just goes as far as a 1963 film could go in spewing adolescent hormonal lust on its audience. It tries to inflame prurient, voyeuristic, forbidden desire (forbidden culturally for teens back in the day, and forbidden for ephebophile adults in any decade) in its viewers, then tries to cool things down with an "aw, shucks - we wuz only pullin' yer leg" regression back to Down Home Values ... only to recharge the rank, dank eroticism to a higher and presumably hotter level, until, FINALLY, Clay-Boy discharges his virginal semen into his rambunctious little filley, presumably barnyard-style.
Note that this "family type" movie is anything but; for all its "Clay-Boy is a-gradyatin', goin' to collerge", its rural church-goin', and full-on "America the Beautiful Sung By The Only Black Person In The Valley" wannabe wholesomeness, its core is simple rutting. Note that there is NO talk of consequences for what certainly appeared to be unprotected humping. The ONLY advice Clay-Boy receives from Head Drunk Of The Family is "next time, find a shady place". When Slut-Girl tells Clay-Head she has a surprise for him, a bit of potential realism arises on the imaginative horizon: perhaps their dalliance has resulted in another pregnancy in our very fertile Spencerland? But no. Slut-Girl announces her school plans just moments before being whisked away by her rich Daddy. Apparently Clay-Head's _cumming_ of age is only that. He's mounted his heifer ... and now he's off to collerge - with a bang! And so our story ends, perhaps leaving the most impressed, dedicated viewers itching for a sequel explaining how the eldest Spencer's daughter gits herse'f mounted deep and hard but doesn't go to collerge cuz she's perpetually barefoot 'n preggers but always just achin' for more 'o the bull.
In short, what a misconceived, miswritten pile of cinematic manure.