Boxing Helena, being rather notorious for being terrible and true, the first 40 odd minutes are purgatory, following our two protagonists, neither of which garner our sympathy. It doesn't help that Sands tells us a lot about his obsession with Fenn, but beyond some voyeuristic watching of her, given no particular reason to understand why he is obsessed except that he is, cos he is, and did you know that he is? Oh and he has some issues due to his parents, which are don't really add anything except to suggest, well, he has deep seated issues. Meanwhile, Fenn's Helena begins as a woman who clearly doesn't care a fig for what anyone else thinks or wants, and you suspect you maybe are meant to be consider her a free spirit, someone who lives in the moment but she comes across a spoiled brat who has grown up to be a spoiled brat. (Noticeably, she lives in a swanky apartment but doesn't seem to need to earn money, lucky Helena). At least you have some vague sympathy for Helena as Sands' Nick truly is unpleasantly obsessive and his attempts to please Helena are so clearly misplaced and you can understand Helena wanting him to just [expletive deleted] off and leave her alone. The latter half of the movie mainly improves, as it delves deeply into counterpointing how men obsess and try and control women (Sands obsequious obsessiveness vs Helena's ex in the shape of Bill Paxton, the more aggressive male who sees Helena as his property), yet despite what happens to her, Helena remains her own person - containing the strength they both lack in terms of character and self-assurance.
Then, sadly, like a film noir from the 40s with an enforced happy ending, Boxing Helena cops out. (You can probably guess how.)
That said the latter half of the film does provide an interesting view of disturbed masculinity and for those expecting violence, gore, explicit sex (though there's a bit of that but all a bit woolly soft-core) considering the subject matter it's mainly absent and mainly a character study.
Sadly though, Jennifer Chambers Lynch hasn't her father's ability as a director, but an ounce - at least as evidenced here. The performances are fine, in some ways better than you might think (though Art Garfunkel's character is utterly redundant) but Sands especially has a character that is so unsympathetic it's easy to consider his performance terrible when he is actually playing the part very well. Sadly, it's not a character that is compelling but it's the one that Lynch wants, the same applies to Fenn. Both do well, but their characters as written, are not the most appealing.