The distinction between a bad and a gloriously bad movie probably just comes down to whether the movie is what you might call "self-aware". I have friends who can't stand the element of self-awareness or anything reflexive in a genre flick, or at least they give me that impression. But a film that is aware of its innately silly premise is qualitatively different than a film that presumes you should be scared. So a gloriously bad movie might be something on the order of Eight Legged Freaks and, of course, Snakes on a Plane. A merely bad movie would be something like The Butterfly Effect though to be fair to this very day I defend Ashton Kutcher's performance. It's not Kutcher's fault the film was as bad as it is. The SCRIPT is the reason the film is as lame as it is.
Since I'm on that topic a bad movie is one in which a mechnanism is needed to accomplish the plot which is abandoned as the mechanism by the time the film is over. Exhibit A ... well, you've already got Exhibit A. Let me break down the breakdown.
Dude has memory gaps and can't explain why they happen. Dude is told to keep a journal to write down what he DOES remember. Mysteriously the dude who can't remember what happened during his blackouts can actually write down EXACTLY what happened and in the process of writing down exactly what happened that he can't remember he is transported back in time to that moment that he never remembered to begin with. Gee, this is sort of like a bad episode of Quantum Leap without the faintest semblance of internal continuity.
Of course flashback after flashback allows him to interact with his past so that he has a multiple choice past but is not fundamentally a different eperson for it. The whol epedophile dad incident actually never changes which gets to another glaring plot problem. When the final home-movie time travel incident happens and Kutcher's character decides he can't have met the girl, ever, he spurns her and is able to somehow have fixed the problems that led to her eventual demise. Sort of. The pedophile dad isn't out of the picture, though, so effectively none of the bause and trauma he (Kutcher's character) is hoping t9o avoid, is ever actually avoided, just his direct presence or participation in the events as they unfold, which somehow fixes everything, or so we're supposed to believe, I guess.
The problem is the film is played serious and not for laughs. Snakes on a Plane has spectacular plot holes that don't beg explanation but merely beg the suspension of a hefty amount of disbelief. A story that just asks you to suspend disbelief is a more honest story in some ways than a story that bets you take the story seriously and then can't keep its internal facts straight. This is why parables work more effectively than didactic tales sent via spam that are putatively based on real events. We can accept the unreality of the parable long enough to accept that it is making a point about the real world. A spam that claims to be about a real confrontation between a professor and a student in a classroopmm about the existence of God or the evils of this or that president that claim to be real events tend to seem like mere parables. The street definitely doesn't go both ways.
This was ostensibly supposed to be about Snakes on a Plane but I suppose it's not now. :)