I've just reread this thread, and I think one of the things that Shreck's take on it underliines is how much it's a movie about atmosphere, about a time and a place and the flow of individual shots, rather than the sort of irritating "is this all a dream?" stuff that seems to get dropped on top of it. The ending obviously has tremendous irony, but the idea that it's some silly Jacob's Ladder style unspoken twist seems rather uninteresting- but really, so does the question of what, if anything, literally happens as depicted, anywhere in the movie. We're seeing through Travis's eyes and must take the work on his terms, which means that we are caught in a hell, and we're gonna die in a hell, just like the rest of 'em, and singling out the ending as being the product of an unreliable narrator ignores how much that's clearly true throughout.
I think Shreck also nails how much the appeal of the movie, to me at least, is the appeal of a really accurate depiction of the sick place in one's (my, really) mind that seems to be the product of some combination of toxic masculinity and exposure to violence and curdled ambition and any number of other factors of living in the place and time that I live. It's certainly a White Boy syndrome- it seems to be something that comes about through a relationship with violence that sees it as deviant and externalized, and not a comprehensible part of every day life, but finds it attractive, rather than repulsive, a luxury that belongs specifically to the privileged, and you could view Travis as an extension of the Nice Guy syndrome that seems to be plaguing teen to twentysomething middle class white boys right now. Somehow his violence stops the movie from feeling like a proto-Curb Your Enthusiasm exercise in missed social cues and awkwardness (Scorsese saved that for King of Comedy) and changes the feeling of identifying with his lead from one of laugh-or-you'll-cry discomfort to one of sickly fascination, a fascination I have a difficult time getting out of my head, for all that I find Travis's primary features of violence, guns, and misogyny hateful and the sole province of people I can't stand in real life.
My girlfriend has watched this movie with me a couple of times now, and while she's someone whose taste in cinema I greatly respect, and which generally overlaps with mine, she can admire the technical film-making here without finding it attractive or wanting to rewatch it at all, there's nothing in her that Travis and his madness appeals to. I'm not sure how much of that is gendered- and surely sociologically rather than biologically determined if so- and how much is that she's from a tiny town in Vermont and seems forever to have lived in an atmosphere of genuine non-violence, while I'm from a less remarkable Floridan suburb and had violence always peeking from the fringes of nearby towns. I do wonder if Travis's racism is something that will date the movie harder than other aspects, though- while America obviously still has any number of people who automatically associate black people, and black people in the city in particular, with the filth and scum that Travis is obsessed with, for me at least it's an idea far more foreign that Travis's anti-social impulse to do something by whatever means he has handy. Certainly, the most horrifying scene in the movie, in terms of violence, is when Travis blankly murders the black stickup man, and absorbs what happens as the shopkeeper beats his body with a baseball bat- it's a scene that belies the movie's reputation for glamorizing violence, as it's almost unbearably ugly in a way the final shootout never is.