Slow isn't so much of a problem. Prague to Vienna is about 4 hours on the train, or it was when I took it back in 2001, 2003 and 2004. But it cost half the price of my 3 hour (non london) Journey home in the UK, and the train itself while old was much more comfortable with those little 6 seat compartments.
Likewise the recent Cartagena - Barcelona train (I got off in Alicante), is much slower than driving, but faster than the bus. yet the train is modern stock, with nice wide seats, that tilt and recline, there is GPS information shown on screen, and even gives free earphones so you can listen to radio channels. It was more bus prices, than train prices too.
Even those ugly Dutch and France non-intercity trains are better than the average UK stock. Only just though.