I haven't seen BESERK! in years, but I recall it being a solid-ish film; certainly better than STRAIT-JACKET or TROG.
According to Wiki at least, both STRAT-JACKET and BESERK! were pretty successful; it's odd that Joan didn't find more work in those years, even if just in horror. Even 4 decades into her career, she was a box office draw.
Oh, yes. BERSERK (though inferior to the smash-and-grab charms of CIRCUS OF HORRORS) is a better produced film that STRAIT-JACKET (well, what isn't?). While TROG only suffers from Partial Monkey Suit Syndrome which seems to wash over the rest of the picture -- what with all its fey Boys-in-the-Band casting choices; otherwise, it mighta worked.
STRAIT-JACKET was a box office hit in early-1964 (a poorly made, terribly-photographed movie with a spectacular premise and fabulous star). But Joan's reputation was suffering not only because she'd disgraced herself with "horror films" but because hers weren't as good as Bette Davis' -- except for BABY JANE and that was
with Bette!
Plus, Bette publicly said in '65 that she "wants out" of the horror genre, despite having had some success in it, because horror is a bit of a trap cinematically. While Joan's attitude, according to George Cukor, was: "I am a star, and this is my next picture!"
Crawford's antics during the BABY JANE Oscar campaign in early-1963 and walking off of CHARLOTTE a year later over "illness" (i.e., fights with Bette) damaged Crawford further, because it showed her willingness to sabotage
studio profits with her shenanigans -- something Davis never quite did. And Joan did it on the final two A-list movies she was involved with!
Still, I want to see a CIRCUS OF HORRORS/BERSERK mash-up with Crawford the rejected and embittered wife of Anton Diffring --- that is what Artificial Intelligence is
really for!