Successful completion of a task v/s user experience

This can be a topic of debate. What is more important in UI designs - the successful completion of the desired task by the end user or the end user experience while doing the task. Well...to me both are inter wined. It is really difficult to separate one from the other. To me both are essential to help the end user do the particular task "efficiently". Now, by "efficiently", I mean:

• The end user completes the task in the stipulated time and
• He enjoys doing the task

I have put more stress on "enjoys". Now, this according to me is extremely important. In the past 7 - 8 years which I have spent designing end user friendly collaterals (presentations, print brochures, product UIs, etc.), I have realized getting into the shoes of the end user (rather looking over the shoulders of the end user) helps in creating designs which provide the end users with an enjoyable experience. Because, only the people who enjoy doing their work are going to produce great output...and in this increasingly competitive world today, "great" output has become a must to succeed.

Now then, it would also be not correct to focus totally on the experience. The UI may end up as an enjoyment tool rather than a utility tool. The bottom line, the objective has to kept in mind. The UI design will not serve its purpose if the end user enjoys doing his/her tasks but exceeds the stipulated time.

e.g. in case of call center operatives: The results of how successful an UI design is are usually measured in  terms of Objective related parameters like time saved in doing the task, more number of satisfied customers (in case of contact centers), etc. I feel, we should also look at "Is the end user enjoying his job more due to the modified UI design?", "Is he/she enjoying their task more because of the change in UI design (assuming that the call center operative likes his/her basic job of talking to customers - has the modified UI design made his/her desktop softwrae using experience more enjoyable?)

All in all, the UI must be intutive, must not compromise on the objectives of the task (stipulated completion time, quality level, etc.) and at the same time provide an enjoyable experience for the end user.