The film is some what dated in terms of production values, but truly the only thing I think that's holding back a better film are the Triffids themselves. The set up for their invasion and encroachment on a crippled global society is pretty intriguing and scary, but the Triffids themselves, like George Lucas commented on scifi monsters in general, aren't "monster enough" to really sell the danger that they present. How you would go about doing that is beyond me, but I imagine it would involve a re-imagining of the botanical menace themselves; i.e. make them more carnivorous, more dynamic, and more frightening as a whole, ergo more plausible in some way.
But, if you can get by that, then this film should entertain. There's one or two hokey moments (the Triffids not withstanding), but the film does try to take a realistic look at a world wide disaster and how mankind of all walks of life would cope. That, and there's a kind of H.G. Wells solution in the end that works both in terms of story and in a scientifically based as well as fictional sort of way.
The acting is actually pretty decent, though there aren't a great number of overly dramatic parts, but the actors really do give it their all with the material they have to work with.
The film is marginally static here and there. I think, as I've stated, as menacing as the Triffids are, they needed to be ratcheded up a notch or two in the frightening-monster department. That, and the current Amazon stream is somewhat low definition and kind of soft, but otherwise an okay presentation.
I think this is one of the good classic scifi films from the 60s that I caught on occasion on weekend afternoons when I was younger. Give it a shot.