I don't think CSI has reached that state yet, though. I'd argue that the seventh season was one of their best, if not their best. Season eight was good as well--the episodes focusing on Warrick were particularly good. Injecting fresh blood into the show--especially via a character with an interesting backstory like Fishburne's seems to have--can really help a show. Nothing lasts forever, but I don't think CSI is done yet. At this point, I'd guestimate a 12 year run. Beyond that, yeah, it might get stale.
Oh don't get me wrong I really loved Season Seven, clearly the best and must see out of the later seasons of CSI
, but I was not so enamoured with Seasons Six and Eight, even if many of the episodes were watchable and a minority of them were outstanding (but we also had stinkers like "Two and a Half Deaths"). I still think the "Golden Age" of CSI
was in it's first three seasons and I want the show to end when it is still good, not outstaying it's welcome like The Simpsons