I have a few thoughts on Aldi, which is where I do most of my grocery shopping.
1) Their chocolate bars are very hard to beat in terms of price and quality.
2) Eggs and milk are among the lowest priced.
3) Frozen food is a great place to shop for one or two, but it is not cost competitive on family-sized portions, which they generally do not have.
4) They change their selection to match the location's clientele. The one I shop at has a selection of hummus, different cheeses, and even full-fat yogurt. The next closest one has ready-made sandwiches and similar deli items.
5) The pre-made pizzas cannot be beat in terms of quality and price. I can buy two for the cost of one from Walmart.
6) The fruits and veggies are priced well, but they're organic and do not keep as long.
7) Meat is hit-or-miss. They have some good stuff and some very average stuff.
8 ) Their soup selection is surprisingly good. No more Campbells or Progresso for me, I'll stick with Aldi's store brands.
To give you an idea about the prices, I bought a quart of full-fat yogurt, a large jar of peanut butter, a thing of cream cheese, a loaf of bread, a car container of chewing gum, and a gallon of milk for $11 yesterday. The chewing gum is $3-4 by itself at Walmart.