It really depends on the individual and your preferences. It’s been a long time since we’ve shopped at Lidl because we’re closer to an Aldi and do our shopping there, so I can’t tell you specifics.
What I can say though is don’t be put off if you can’t get your head round the lack of choice at first - once you get used to that it actually makes life a lot easier and generally cheaper too.
If you try something (pre-made things in particular) and you don’t like it, just don’t buy it again! Everyone has slightly different tastes and asking what to buy or not buy doesn’t take account for that. I always try own-brand things (ketchup, cereal, baked beans, whatever) and give it a good few weeks to try them because sometimes it takes time to get used to a different texture/flavour/whatever. If at the end of the bottle/box/tins I still don’t think it’s as nice, I just don’t buy it again. So I’m happy to buy own brand baked beans, ketchup, other condiments, but if I’m in the mood for cornflakes (which I can’t have often anyway) I know that only Kellogg’s will do.
We don’t buy ready meals or pizzas etc so I can’t advise on those. Again you’re better off just trying it.
I think we found the meat at Lidl of better quality than Aldi IIRC (generally speaking). We buy all our meat from local farm shop now so I can’t really say what’s best at Aldi. I do still buy chorizo, bacon or pancetta and sausages from there. And ham/salami once in a while (we don’t eat it often)
If you’re a reasonable cook and can go with the flow on changing meal plans slightly if it turns out they haven’t got X Y and Z that’s on your list then I think you’ll find it just fine.
Cleaning products, washing detergent, dishwasher tablets, all that stuff, the own brand works brilliantly.
Wines, cheeses, olives and antipasti, etc, there’s plenty of that of good quality.
Be aware that branded goods are often same price or sometimes quite a bit more than in supermarkets.
Watch out for the aisles of doom!! Only buy things if you actually need them. You can find really good things there though.