I can answer this;
We took Amtrak from LA to Seattle. It took about a day and a half and was really a fun and enjoyable way to travel.
BUT....
We were frequently shoe-flied to yield to cargo rail trains. The conductor told us that was because the AMTRAK train was shorter and the long train would not fit on the shoefly track. That is technically true - but it tells you where the priority is also. Freight trains, and not passenger trains, make far more money. It is not uncommon for AMTRAK trains to be delayed for cumulative hours because of all these yield stops.
The other problem, and I am specifically referring to California HSR in this instance, is that the new rail line is routed by politics and not common sense. Take a look at a map of California and you tell me - why is the CA HSR going up Hwy 99, paralleling and crossing the existing towns, bisecting farms, andcrossing back and forth over the existing AMTRAK San Joaquin line the whole way, when the far more direct route is up I-5, where there are far fewer ROW issues and far more existing public ROW where the train could run? Reason is the representatives of the farming towns in Fresno, Modesto, and other (sorry, but let's be honest) meaningless stops would not vote to even put the project on the ballot without these stops. But here's the thing; those towns already are serviced by AMTRAK, and HSR is decidedly not "high speed" when it is stopped at all those towns. Common sense says it should stop in Bakersfield to make that connection to a currently very under-utilized San Joaquin line - but no. And this ridiculous politicking has wasted tens of billions of dollars so far, without a single mile of track laid, and what public confidence it had, eroded to all but the most ardent supporters.
LSS - politics have made CA HSR untenable, and I am certain that is not the only example. Even Brightline, that has received largely positive reviews for the Miami to Orlando route, is currently stalled for the remainder of the route to Tampa, because politics of the route out of Orlando. Don't take my word for it, Brandon has it expertly covered on Mickey Views - really some of his best work, check it out.
Such is the state of rail travel in the US...