It has to be said, though, that for most users of what is now the Northern Line, the present situation is wildly better than the pre-1979 situation. Merseyrail is really quite a good operation, and one of the few local rail services that would come close to meeting muster in a comparable large German city. And it's about to get new EMUs meeting that sort of standard, too.
Yes, the direct Scottish services were lost, but those could just as easily run via Wigan (and are doing).
That said, the stations are all very 1970s and utilitarian, even post-tarting-up. I'd love to see Liverpool Central rebuilt again, only this time making it more impressive with both a new ground-level building to replace the run-down shopping arcade, plus opening out the Northern Line platform area to have an uplit, cleaned concrete ceiling and feature platforms (a bit like the Haagse Tramtunnel, maybe, which has wooden platforms, though for fire safety it'd likely have to be wood-effect tile), perhaps with impressive murals, a bit more like the disused platform at James St and less like the present dump.
I love the way each station in Hamburg, a comparable global port city (at least historically), has its own character and style, and I'd love to see that unseat the boring utilitarian nature of Merseyrail's underground stations.