Yamagata is only 2.5 hours away from Tokyo by shinkansen (rapid express). The distance between Tokyo and Yamagata is approximately 400 km, so they are not far away from each other. Yet, they are so different.
First off, the time flown in Yamagata is much slower than that in Tokyo. I just heard from my American friend living in Boston that everything was slower when he travelled to Denver. It is about the same. If you like being surrounded by skyscrapers, Yamagata may not be a place for you. In any case, however, it is worth a visit (whether it is a long or short one).
Second, people are nice. I am not saying that people in Tokyo are not nice - they are. However, people in Yamagata (let's say Yamagatans) are even nicer. If you live in Yamagata, it might happen that you do not buy vegetable or fruits often, because neighbors give them to you. Yamagatans may be a bit nervous when you first face them, since it is not so much a touristic place. Yet, once you talk to them, you will see what I mean.
Last but not least, what you consume in Yamagata are amazing. The air is clean, the local food is tremendous, and sake is the best. I cannot express enough how good they are, so I put the pen down here.