Empress was designed as a very cosmetic material, but it was a little
low on strength.  Still, I know many dentists have used it for front
teeth with good success.  I believe (not sure) that Empress 2 is
supposed to be stronger--it may be similar to Procera, which certainly
is stronger than Empress.  One of its selling points is that it can be
cemented with traditional cements, rather than bonding in place
(required for original Empress).  I've done Procera restorations and
they are plenty cosmetic.  They supposedly aren't as beautiful as
Empress, but I really can't see much difference.
    None of these materials are indestructible--not even porcelain fused to
metal.  I have a patient who fractured the porcelain off a bridge
abutment of a porcelain/metal bridge two weeks ago.  The bridge is maybe
2 1/2 years old.  I tried repairing it in the mouth, but my luck with
these intraoral repairs isn't good, and the bridge will likely have to
be replaced.  It may have failed because the patient bit on something
the wrong way, or there may have been a flaw in the porcelain firing at
the lab.  You can't always tell why porcelain fails, but all of them
fail occasionally.
    What I don't want to do is ask too much of these materials.  Most of
them will work with single crowns; though In-Ceram has been used for
multiple units (bridges) I am far from ready to use any of these
materials for bridges--I've heard too many sad, sad stories.  But unless
you have habits such as chewing on ice, chicken bones or blasting caps,
all of these materials have a high likelihood of holding up for single
crowns.

HTH,
Steve