Xbox is successful in that it has a large mind-share in the hard-core gamer community, but financially the project is still a failure. Had Microsoft decided not to begin the Xbox project 10+ years ago, it would easily have a few more $billion in the bank today.
Contrast that with the Wii, which, along with the DS, has added billions of dollars in profit to Nintendo's coffers over the past few years alone.
Now that Xbox has established itself, the next decade will show whether or not the system is net-profitable, or whether the project never should have started to begin with.