I travel by train a lot both in UK and Europe.
UK long distance services are, at best fit, for purpose. Compared to Netherlands, Germany, Switzerland, Austria, and France (when not on strike) the comfort, speed, space and ride quality are poor. Punctuality is acceptable, and generally so is staff attitude. Rolling stock is often shabby, overcrowded, and dirty. If you pay a low fare, this might be acceptable, but for some of the extortionate unrestricted fares, it’s not. For example, a journey I do frequently from the NW to the SW prices at anything between £26 o/w in second class to £265 in first.
Catering options are very poor on a lot of UK services, with those I’ve mentioned above all doing far better, except France which is, perhaps surprisingly to some, abysmal, unless you consider €12 for a piece of frozen bread with burnt cheese on it, and 500ml. of inferior beer in a squishy plastic cup to be compatible with a nation that unjustifiably prides itself on being leaders in ‘cuisine’. Those days are over.
It’s easy to book using various websites in the UK although you have to know a few tricks to get the best fares and connections, as there is very little transparency. By contrast, as other have said, the DB and SBB sites are excellent, and although limited, so is NS.NL. The SNCF website is, like most French websites, overengineered, dysfunctional, and inefficient. Once you get to the right place though, it delivers and the ticketing machines work.
Italy’s train services (apart from the excellent Freccia services) are appalling, WWII rolling stock, filthy, smelly, and decrepit specially on some local trains. Italy is the only country in Europe where I have felt unsafe on a train. The Trenitalia website is, if possible, worse than the SNCF one and the ticketing machines rarely work.