I ride amtrak from Phila. to DC all the time. VERY good ride, much faster than driving. It is pricey though.
For the regional lines, there is far less ridership, so there is much more space, and things can be more pleasant. Since there is AC power, a laptop or movie player can be used without issues.
That said, the regional trains stop often, and so are much slower. Between DC and Phila., the difference between the regional and the express is about 15 minutes, and about 30 min to 1hr faster than driving. For the regional from Philadelphia to Pittsburgh, there is no express, but the train is a good 2-3 hours slower than driving. Then again, you can do work or enjoy yourself the whole way.
Regional trains are pretty cheap, its the boston-DC area that is $$$, because lots of folks use it. Given the cost of tolls and wear and tear, the train was a cost-effective way of doing Phila.-Pittsburgh before gas was $3.40/gal.
JMH