I assume you will be going to Chicago? You didn't mention the time of your trip, but if it will be later this year, you will have diminishing daylight. It will be dark when you leave Denver and no light until you are in Iowa. So the scenery will be Iowa and Illinois, much of which you may be already familiar with. Of course, you will see some new views from the train that you don't get by car.
If you explore this forum, you will find tons of opinions about the food, so I won't dwell on that. Lots of people like it and others see room for improvement. You will learn a lot by reading some of the food related threads. But the experience of eating in the dining car is itself a bucket list item for many people. I recommend it if you haven't done it. There is talk of changing the dining services in the coming months/years, so if the dining car appeals to you it may be a good idea to take a trip sooner rather than later.