To me Galileo's Bar and restaurant is currently the best party scene in Nairobi. Great ambience, affordable local beers and very decent crowd. Galileos is basically two clubs in one.
One side has a sizeable dance floor while the other lounge basically is kind of a sports bar. Be careful to get there a bit earlier, possibly around 10pm because parking can be a problem.
The late you get there, the further you will park your car. Sometimes it can get really congested which could be a turn off.
Otherwise, it's a great place! Loved Galileo is one of only a handful of clubs that is aimed at adults.
The crowd is mature and the music is excellent, a nice mix of Kenyan, dombolo, kwaito, hip hop and of course all the pop hits.
There's a main dancefloor with lots of seating and there's a VIP section in the back, also with it's own dancefloor. The main area is way more fun.