I took the Amtrak train (California Zephyr) from Colorado to California - roughly 32 hour trip. It was kinda sucky, though, because due to a freight train derailment, we couldn't take the usual route through the Rocky Mountains, which is supposed to be very scenic. Instead, we had to go hundreds of miles through boring grazing land and plains - lots of cows.
But it was alright, you can walk around at will the whole time, hop from car to car, sit in the observation deck, have lunch or dinner in the dining car (bring money). But for $86 (regular price of $108), I could have probably found a competitive one-way air fare and made the trip in 2-1/2 hours or less. 32 hours vs. 2-1/2 hours.
Depends on how fast you need to get where you're going. Most people aren't traveling just to 'see things' in between their departure and destination. They're traveling to get some place. Its much more expensive to stop along the way, stay the night, etc.
One of these years, I intend to do the National Rail Pass thing with Amtrak, for around $400 you can ride the train anywhere in the US for 30 days with unlimited stop-overs. Go anywhere you want.
The North America Rail Pass includes the US and Canada for around $600.