Trains in France are not vastly cheaper than the UK, but the service pattern is awful outside the very main routes. Often huge gaps in service for parts of the day and non-clockface timetabling. Seems to be very poor utilisation of rolling stock, with a lot of the stations having trains sitting for hours doing nothing (which should really be operated more intensely to give a better service pattern).
DB has horrendous reliability problems, basically the entire network gets something similar to TPE on time performance (the worst performing TOC in the UK). ICE/IC trains are also not particularly cheap for on the day travel.
Spain's high speed lines are excellent and very cheap. But outside that the network is incredibly limited and slow, so much so that buses will almost always beat the train in journey time.
Netherlands is good, affordable, frequent services and reliable. I think NL is the only country I've been to where the system is noticeably better than the UK across a lot of dimensions.