Interesting, i am in the opposite situation. Using the deutsche bahn for long distances is often horrible so I never thought I would miss it but omg I really didn't have a good experience with Uk trains. The ticketing is complicated and the trains were often so unbelievably dirty and run down. Never had this experience in an ICE. Okay there are sometimes issues like the toilet boing out of order or the restaurant closed but the train is usually clean and fairly nice. And while the delay wasn't massive I still had delays. It's also sooo slow, there's no high-speed train. Last time I took the train from southampton to edinburgh and it really took forever and I was soo slow.

Even Edinburgh-London is slow! It's a similar distance than munich-berlin, a train I often take. In germany these are sleek, clean trains that take just over 3 hours, with only one or two stops with the sprinter. The train in the UK takes around 5 hours, significantly longer. I can do 3 hours on a friday evening work and arrive not too late to then meet friends for drinks, you can't do that with 5 hours.

And not only ICE, it's the same experience with regional trains. I used to live in Baden-Württemberg and took a lot of regional trains. I didn't think I would miss it with the delays from the new central station that they've been building for what feels like forever but now I do.

There are many things that the UK does better than Germany but trains they manage to do even worse (or maybe its not that bad?)