We took our first Amtrak trip this summer, LA to Seattle on the Coast Starlight, the Seattle to Chicago on the Empire Builder, and finally the Chicago to Cincinnati on the Cardinal. Nearly 5,000 miles over two and half weeks -- we stopped in San Francisco, Seattle, Glacier National Park, and Chicago along the route.
I asked for advise here and on several other forums before we left, some of which was good, some really didn't apply as we're in our early 40's traveling with a 10 & 11 year old -- rather than traveling a retired couple.
My advise would be:
1) The car may or may not have random sounds which you may or may not be able to stop. Take a small roll of duct tape and be willing to tape things down which rattle. Be prepared with a set of ear plugs too, and perhaps a low dose sleeping pill or two. We had 10 different cars during the trip (2 roomettes per leg), about half of which had something that needed a bit of tape to keep quite, and two which had a screaming pig in the wall that yelled out with every turn -- well maybe not an actual pig but it was a heck of noise with no way to stop it or move rooms -- take ear plugs!
2) The quality of the car staff makes all the difference in experience, we had some that ran a tight ship, super clean bathrooms, fresh coffee, super helpful, made up our rooms on our schedule, etc., and others what weren't anywhere close -- bathrooms that could have been fresher, coffee that reminded me of the Navy, and room resets when they wanted to do it, even when we didn't want it done -- turned down my own rooms twice because I didn't want to go to be at 8pm. I'm not a 9 year old. If they are good tip them, first time you can, a $10 bill goes a long way.
3) The train will get you there, but it goes when it wants (which sometimes means it doesn't) be prepared to relax and enjoy the ride.
4) I took 6,000+ photos, along the trip, mostly from inside the train. It gives a unique view of the country and one that as a model rr guy are hugely helpful -- what really is along the tracks (hint: it isn't ice cream shops), there a tons of great buildings, signs, bridges, trains on side tracks, and natural wonders too. I spent nearly the whole of the trip glued to a window, camera in hand.
5) Since you're on board for plenty of meals, figure that out early. On our whole trip every lunch and dinner entree came with succotash, great, unless you order pasta which has big scoop of it on top. They put it on every dish, regardless of if that made any sense or not, nope, everyone gets succotash! I ate my weight in signature steaks, they do a nice job with those -- nice basic steak, small baked potato, and succotash. My wife points out even dinner and lunch salads have a scoop of succotash. Just a heads up.
6) Be prepared to step off at every fresh air stop, there will be plenty. This was a highlight, just getting off for a couple mins, walking the distance of the train, breathing in some fresh air, and great chance for station photos. These breaks aren't long so stay close!
7) Rails and trails is great! We would sit in the coach dome car and listen to the guide narrate the trip, they have prepared guides they follow, it was wonderful to know what one was looking at -- on you're left is XVS on coming up on your right will be ABC, etc. This is only done in the coach dome car, you have to ask the car staff or listen, since you're in the sleepers.
8) Unlike flying you can bring as much as you wish in terms of water, pop, wine, etc., although this can only be consumed in your room. We went through a lot of water and few bottles of wine along the way.
Hope you have a wonderful trip! While this was our first trip, and no one other than me has any love / like of trains, it will not be our last. My wife, wasn't thrilled about all the train travel when we planned the trip, but by mile 5,000 she said she would take another similar trip any time.