I"ve been recently on a stag do and it is a top city
Park Inn (next to alexandersplatz station) has a casino that does poker tourneys
next stop west on the S-bahn is Hackescher Markt which has loads of bars and a top brauhaus (beer and steak!)
next stop west is friedrichstrasse, which can be a good starting point of a walking tour (brandenberg gate, reichstag, holocaust memorial, berlin wall, checkpoint charlie)
When I went, I stayed in the old East, so I cant comment about the west (charlottenburg is apparantly good though)
Have fun!!