I have been to Joy Tsin Lau twice, with mixed reviews. It is a very popular restaurant located in the heart of Philadelphia's Chinatown. Thus, it is very convienent for visitors staying downtown near the Convention Center - where there are not many nighttime dining options. While it comes highly recommended, my experience at Joy Tsin Lau has been very hit or miss.
Joy Tsin Lau caters to a largely local clientele. The staff is friendly, but many of the waiters are not fluent in English. Be prepared to be patient and you will be able to communicate. The decor is traditional Chinese/Vietnamese. Fresh seafood is kept in tanks on the back wall. A karaoake machine will intermittently play a bi-lingual Happy Birthday song (!). They are able to accommodate reasonably-sized groups on short notice.
The menu selection at Joy Tsin Lau is large; you can find any of the usual Chinese selections as well as more unusual offerings. The first time I went to Joy Tsin Lau, I found the food to be standard Chinese fare. I had sweet and sour chicken, which is a very simple dish. It wasn't impressive or awful. The second time, however, myself and my group were completely underwhelmed by the preparation and service (which was unbeliveably slow). In fact, several of us got sick from chicken dishes and the duck dishes took over an hour to arrive. Due to that, I cannot highly recommend Joy Tsin Lau.