Hardware sales have slowed down (Halo 4 should help the quarter it's in but without a price cut there's probably no real chance of beating last years numbers for that quarter) but in terms of software and Xbox Live the system is doing well considering its age.
Lets have a look at some of the biggest third parties out there...
UBISOFT
ELECTRONIC ARTS (Notice the difference from Q4 FY11 and Q4 FY12)
TAKE TWO
ACTIVISION
Add to that the fact that Xbox LIVE has grown and games like Minecraft breaking XBLA records and it's pretty obvious that the system is going very well.