That depends entirely on the criteria being used to determine the console's success. Comparing the PS3 to its predecessors would lead one to say it's definitely failed to live up to expectations, but looking at the PS3 in a vacuum could lead one to say it's been fairly successful.
In the end it's making money and providing me with fun games to play over five years after launch, and that's pretty good when compared to many consoles of the past. So for me, yeah, it's a success. But that's only based on my own personal barometer.
Though there's no doubt that Sony (and everyone else prior to E306) were expecting it to be far more successful.
Edit:
Really, labeling it a success or failure seems kinda trivial.
We know the marketshare the PS1, PS2, and PS3 held during their respective generations. We know the rough profit and loss for SCE for each year since '95 or so. We know how long the PS1/PS2 were able to sell on the market, their peak years of sales, and so on and so forth. We know that the PS3 is financially viable and has enough demand to continue selling at this time. We can analyze publisher support for the PS3 compared to other consoles, and we can do the same with actual software sales. And we can use all of this information when gaging what actions SCE may take in the future.
Applying a subjective term like "success" or "failure" to the totality of this information doesn't change any of it, nor does it add to or subtract from the usefulness of such information. Thus, we're all labeling the same exact information in different ways.
Though I suppose it's about the same as saying "I like band X". Music doesn't change depending on the listener, and subjectivity exists for a reason.
...I need to stop letting my mind wander like this.