Gambela is a region in the very west of Ethiopia.
Gambella is the region of Ethiopia's National Park with the greatest numbers of wildlife, Gambella National Park. Famous for its White Eared Kobs the world's second most abundant migratory mammal, it is also know for its buffaloes, Giraffes, Nile Lechwe, Warthogs, Topis, Waterbuck, Roan Antelopes, Burchell’s Zebras, Bushbuck and Reedbuck. Reasonably priced service providers include Ecotravel Ethiopia ☎ ++251 (0) 911-440-915" 
Gambella Town is roughly 45,000 people and situated astride the Baro River. It is a lively town, with restaurants and dance clubs aplenty. The dry season and wet season bring out remarkably different characteristics, much the same in other parts of Sub-Saharan Africa. There are several people groups, but most prominent are the Nuer, Anuak and Habesha. Each have some cultural differences that make them interesting: one can visit the model village on the western edge of town with a guide if they would like to know more.
Gambella Airport is a traveler's best bet. Direct flights from Addis are reasonable and only 2 hours. If flying is not to one's liking, there are buses, but they will take much longer: 2 days, at least, from Addis. Occasionally, the roads between the capital and Gambella Town is closed by the government, so flying really is the best option.
One must take local transport or arrange for pickup from the airport, as it is approximately 30 minutes from the town...in the dry season. Prices negotiated at the airport will be much higher, especially for "faranj" (stranger, non-Ethiopian), often as much as 3 times the usual price.