I have a number of controversial opinions that'll probably wind everyone up:
1. Britain's railways are soulless and boring - lack of uniformity, lack of national train builders, train after train of boring, identical multiple units. Just awful. The Great Eastern has been ruined in the past few years with the introduction of the Stadler trains, the route had so much more variety in traction before and now its the same train to Southend/Clacton wherever and the longer, weirder looking ones that run to Norwich. Don't even bother remembering the class of new trains any more. Much prefer Amtrak, Renfe or the Japanese railways.
2. Beeching was awful - I'd rather risk a world in where Beeching didn't exist and the railways had to find their way without him, because I really think his cuts impacted the soul of the country. For whatever reason, the British country branch line was something of a great comfort in the national psyche, possibly in the post-war period it was a reminder of a more stable time or at least created a form of escapism for a traumatised country. Taking that away without much obvious care has left a permanent sense of discomfort and soul searching in railway circles and the wider public.
3. We were too quick to forget Waterloo International - I think the Eurostar has lost a lot of magic and romance compared to how it was in the 90s. Running the Eurostar, a quarter of a mile long high speed train, that literally went to another country, impeccable feat for an island nation, past signals that pathed a train to Orpington just before pathing a Eurostar to Paris, is amazing to think about. Sure, we didn't build a dedicated high speed line from the Channel Tunnel immediately, but adapting our existing railway for use of "Super Trains" to the Continent, looking back, was a pretty epic thing to do. HS1 may be fast, St. Pancras may be grand - but its not...interesting. I can't stand on the High Street doing my shopping waiting for the long, roaring train to Paris fly overhead, unless I pay for a Javelin ticket and watch the trains in the bowels of Stratford International station.
4. Network SouthEast was great, but I'm not sure if I want it back - I find that whilst the NSE livery looked perfect on most stock, for termini like Waterloo, where every train was in NSE livery, it could begin to look a bit overwhelming.
5. The Elizabeth Line is...not that great - the class 345s look stupid, the stations are bland and identical (unlike the Jubilee Line stations which are all laid out slightly differently) and the ride is boring. Compare that to the Jubilee Line where you have far more junctions, the clatter of the shoes over the live rail, the sound of the 96 stock traction motors -it's still an epic ride 20 years later. I don't know, maybe its because I'm autistic and I care far more about trains in a level of detail most people find ridiculous, but I was pretty disappointed with the EL when I rode it on opening day last year.
6. The Southern Region is the best Region. End of.