I've been there, had a good time. Knew people who are from there and could show me around which helped. The currency is the American dollar and you shouldn't have too much problems if you don't know spanish. Quite a bit of night life, lots of good bars and restaurants. The waterfront is well maintained and has lots of old style architecture and makes for nice walks. The old panama city ruins Panamá Viejo is a nice place to go see for half a day. There is of course the Panama canal to go see and going across the two bridges that join the continents is a nice sight.
Clothing is ridiculously cheap for high quality stuff (though some places are still expensive if you shop at the wrong places).
If I think of other things I will add them later. Let me know if you have any other questions.