There's nothing interesting in Plymouth.
Other than the sound, the hoe, the barbican and the beaches/cliffs around it. Not to mention Dartmoor and Cornwall just to the west. More interesting than London TBH...
I always find Lidl and Aldi (in this country at least) resemble dumps inside with stuff piled up or thrown in big/wrong containers. I'm not sure whether it's a lack of staff to clear up or the people that mostly frequent them. As for food I'm not sure. I always base quality of food on how much wheat stuff contains. Its a cheap filler that is used to bulk stuff up as cheap as possible. Asda and Morrison's are awful, everything is full of it, for example Morrison's don't do a single beefburger (no, not even the 100% Beef...) without wheat in. Iceland is just as bad. M&S on the other hand rarely use wheat in anything unless they need to, almost all beefburgers and sausages don't contain any. Tesco is ok, as are Sainsburys, Waitrose is in between Sainsburys and M&S. You get what you pay for...
Aldi and Lidl in Germany on the other hand are nice shops, still "budget" but more like Tesco etc.