I've driven over Marias Pass a million times, in all seasons ... and as lovely as the trip is, I admit that it's gotten old hat by now. Mostly when I drive it, I'm just trying to make time.
The railroad line used by Amtrak's Empire Builder also crosses Marias Pass, of course, but I've only ridden a train across the pass a few times. And even though the tracks nearly parallel the highway, differences in elevation and angles make the ride a wholly different experience than the car trip. Much more interesting, I think -- and of course the views are easier to appreciate because the speed is lower and one doesn't have to think about driving.
My train ride over Marias Pass last week was cold and grey, but still thoroughly spectacular. Here's a shot from the trip, taken high on the western approach to the summit.