Since the "Z" trains between Shanghai and Beijing are overnight, you don't really get to see much in the winter, and only a little in the summer. But you do save a night of hotel each way.

The soft sleepers are clean and comfortable, but you do have to share the cabin with other travelers (each cabin sleeps 4).

There are pluses and minuses for the train, and they are not for everybody. But they are in generally well run.

As for train travel in general, because the costs are pretty cheap in western standard, one should always get a soft sleeper/seat if available.