Having recently ridden Amtrak, easily the worst thing about it is the fact that they've decided to go with an airline style boarding process where the platforms are treated as a secure area and everybody has to single-file get their ticket checked to get onto a platform.
The whole advantage of a train vs a plane is that a train has many doors, allowing a lot of simultaneous boarding to happen; and they also already have conductors who check your ticket to make sure you are getting into the correct car, and another ticket check once the train is in motion. It would be significantly better at major stations to just have conductors at every train car on the platform in parallel doing ticket checks, rather than just have one funnel.
The whole advantage of a train vs a plane is that a train has many doors, allowing a lot of simultaneous boarding to happen; and they also already have conductors who check your ticket to make sure you are getting into the correct car, and another ticket check once the train is in motion. It would be significantly better at major stations to just have conductors at every train car on the platform in parallel doing ticket checks, rather than just have one funnel.