I can remember shopping (or trying to) in Leeds city centre about 1998, so within five years of the laws being liberalised, and it was a very mixed experience. Because of the position regarding contracts of employment, it tended to be largely junior weekend staff working so the standard of service was unpredictable to say the least.
In the 18 years that I've lived where I do now, the Sunday service to Leeds has doubled in frequency and then had a couple of later runs added to ensure a half-hourly service until the end of shopping hours. I don't tend to do very much on Sundays myself anyway, but it's probably right that twenty years on and with internet shopping now normal, it's right to look at things again. There's a greater proportion of the population for whom Sunday has no religious significance, shopping in itself has developed as a leisure pursuit and online shopping has changed everything. If I wake up on a Sunday morning and decide that I'd like to see a particular film or read a particular book, I can either wait for the window of opportunity when the shops are open or I can download them there and then.
Interesting to see how the Germans have worked around their Sunday traing ban too- every time a new railway station or airport terminal gets built, it comes with a shopping centre bolted on "for the use of travellers", although from what I could see passing through Dusseldorf a couple of years ago, the airport shopping was being promoted as a leisure destination in its own right.