It's delivering what they want and need in an enjoyable and engaging manner. Client experience is not just servicing a need, but making it a great process. It should be something they enjoy doing and and something that is not a chore. The best way to do this is to have a well designed product with an amazing user experience. If you give them an easy and enjoyable way to do their task then this is something they will not only come back to, but something they will be more likely to share with others.