Top Shanghai is my favorite Shanghainese restaurant in the lower mainland by far.
The restaurant is not elegant or high-end, and you shouldn't come and expect it to be. The place is in a small strip mall on no.3 road, so it's quite cramped. The doorway doesn't have a lot of room, so often people are crammed at the entrance trying to get a seat. The place is ALWAYS packed and noisy any time I go, but you won't hear me complaining. It's no different than most Chinese restaurants.
If you're going to Top Shanghai, go for the food and only the food. The steamed juicy buns are unbelievably good. I'm from Shanghai, and only at one place in Shanghai have I had better. Other favorite dishes are Szechuan beef noodle soup, fried rice with dried scallops and egg whites, crispy chicken in soy sauce, crispy rice with soup on top.. I could go on and on. If you're interested in trying something very different, I'd recommend the cold cut mutton. It may be an acquired taste, but it won't be like any western methods of cooking lamb you've tried. Everything is also really cheap! It's so much better value (and taste) than Shanghai River without being pretentious.
The service at the restaurant really isn't horrible. The waitresses are just overworked due to the constant busy volume, but I've never seen them be rude. Ordering in Mandarin / Cantonese / Shanghainese will probably help a bit for them to get your orders right or get the bill to you faster, but even in English I've never had any real problems there. Table sharing is sometimes necessary unless you always go with large groups, but they don't force you to share a table. If you don't want to, then they will let you wait until a smaller table frees up.
It's a great restaurant and there's good reason it's always so packed. Try going at non-peak times if you're trying it for the first time.