Plan to entertain yourself as there is not much to see or do. However, due to the many expats including many Kenyans, Ugandans and the hundreds of Westerners there are numerous bars, restaurants and nightspots. There is something going on most weekends. You can also take a boat trip on the Nile, go fishing, go jogging, and there's a Hash House Harriers in Juba.
But even then if coming here to work for an extended period, bring out lots of books, DVDs, etc.