I have flown this serveral times and agree with BlondeBomber 100%.
Economy is fairly comfortable - good FAs, etc.
In my opinion, Yaounde airport is less hastle than Douala. (But Douala is far better now than it was years ago). In addtional to the airport tax BlondeBomber
mentioned - it would be a good idea to have some CFA apon arrival to pay a porter at the airport in Yaounde. Passengers are generally expected to pay a porter - say 2000 CFA (aporx 4 euros). The porter will try to get as much as he can though.