This is a 100% ethnic store, they really only target their Polish customers. If you're not Polish then prepare yourself for a bit of a culture shock, but never complain. If you don't like it, then go somewhere else. This is not a one size fits all store.
If you're Polish, you will be delighted. There is no better selection or better prices anywhere else in Chicago. You won't mind the crowded store. There is a good selection of made in Poland groceries, and that's worth a trip from miles around.
The people who work there are not unfriendly, in fact they are extremely friendly. Unfortunately they, in general, do not speak English. So if you don't speak Polish, then you can't communicate, and some people may take it as being rude.
My advice is, adjust your expectations. This is like visiting a foreign country. If you don't like it, don't come here. But if you show respect and make an effort to adjust, you will be rewarded with the best quality Polish groceries you can buy in Chicago.