I enjoy properly presented "What If? scenarios.
If you say, "What if the oceans rose 300 feet?" and then in your story fail to account for certain key logical conclusions of that "What If?" (for example, you could make a big deal out of the symbolism and imagery of sunken present day cities, but fail to realize that people couldn't realistically still live in those cities), then no, I'm not going to enjoy it.
I already stated a few ways to make "What Ifs" enjoyable. If you're writing a story that isn't concerned with matching reality or making logical sense, there are ways of signalling this fact to your reader and in effect asking them to suspend their disbelief.
Stories like Harry Potter work because all the impossible things are easily explained with one word: magic! So long as you keep your magic at least somewhat internally consistant, it's pretty easy to get even the most unwilling of readers to suspend their disbelief with magic. If some absurd Deus Ex Machina crops up, like the Sword of Gryffindor appearing out of thin air at just the right moment, we're okay with it because magic can do that.
Stories like The Hitchhiker's Guide To The Galaxy work because they don't take themselves seriously and the reader is too busy being amused to care. When a Vogon Destructor Fleet shows up out of nowhere and just sort of floats in earth's atmosphere despite gravity, we suspend our disbelief chiefly because we're already busy laughing over the absurdity of everything that's led up to that pont. We're not concerned with how they're just hanging in midair, because 1) they're advanced space aliens and 2) it's not important to the story or the humor.
Stories like The Matrix work because while the logic of the drama is spotty at best when you stop and think about it, the creators go to pains to not draw your attention to it in any way. It doesn't matter that the robots using humanity as a fuel source would be completely energy inefficient, because that's only one ultimately unimportant detail that we learn in the course of unraveling a much larger mystery. It also helps that they hand wave it, with Morpheus saying the machines combine this technique with "a form of fusion". They also then immediately move on with the story and never mention anything to do with the human-fuel scenario ever again.
It's fine to write stories that involve unrealistic things, or which don't have perfectly consistent logic. But when the basic premise of your story makes absolutely no sense, you've got a problem. Harry Potter might have a lot of little plot holes or logical inconsistancies in places, but the core concept of a hidden magical world isn't hard to accept. The Hitchhiker's Guide To The Galaxy certainly isn't the height of realism, but the core concept of a human everyman being dragged into a weird and hilarious alien universe is likewise easy to digest. The Matrix breaks down a bit if you try to connect all the dots with an expectation of total realism, but it's central tenet is that reality is an illusion and that the actual world is quite different from our own.
But when the basic premise of your story is that someone invented a Perpetual Motion Engine and decided to make a luxury passenger train out of it instead of using it to revolutionize human industry and production; and then a sudden, inexplicable, unavoidable global apocalypse destroys all human life except for a small group that take refuge on the train and absolutely no one else anywhere else survives; and then for some reason the Perpetual Motion Engine only operates if the train is in motion...
No, I'm sorry, you've soared past the limits of willing suspension of disbelief for me and many others. The entire story hinges upon such singularly illogical compounded nonsense that it doesn't work. The basic premise is just too profoundly unbelievable.
Worse still, it utterly falls apart if you try to remove the absurd pieces. Take out the "need" for the story to take place on a moving train, and the conflict evaporates. A bunch of apocalypse survivors in a much more realistic shanty-town or a bunker or other safehaven, living off a Perpetual Motion Engine, doesn't have the same Catastrophic Countdown crutch propping up the conflict. Take out the Perpetual Motion Engine and there's no way you could keep a train in motion in addition to providing warmth, food, and light for people in the middle of a mini Ice Age.
No, the story just asks too much. It requires you to accept that not only was there a global apocalypse, but also that it was too sudden and unexpected to be prepared for in any way; that humanity has invented a Perpetual Motion engine just recently enough that there's only one working example; that this one working example was put to the absurd usage of powering a luxury passenger train; that this train was conveniently designed in advance to deal with several-meter-deep-snow-covered tracks via special precipitation vaporizers; that the only survivors of the entire human race just happened to be people who took refuge on this train; that these survivors just happened to be conveniently stratified by wealth and status; that unlike in real disaster scenarios where wealth and status become meaningless in the face of survival, for some reason the wealthy elites are allowed to assume command of the band of survivors instead of a competant, cooperative leader with actual skills who can actually get things done; that once in power and beginning to abuse it, the wealthy elites don't get deposed and scragged by the majority masses...
It just goes on and on with unbelieveably unrealistic nonsense, and you have to accept all of it for the basic premise to work. No thanks.