"But, somewhere around the turn of the century, I lost interest. The show became less and less surreal."

"Real celebrities started showing up, and I winced as Dave would suck up to them. Suddenly, everyone had a perfectly polished, self-deprecating anecdote — invariably meant to prove the utter fiction that Celebrities Are Just Like Us — that sounded suspiciously crafted by a team of writers. Suddenly, each episode had as many as three celebrities, with Letterman being unctuous and insufferable and fake-laughing his way through every minute. At times Dave would turn depressingly earnest, particularly when he thought he had a Deep Political Point to make.... His comedy started to sound like everybody else’s, with the same potshots at the same easy targets. His act sounded less like dada, more like Dad. Letterman was the barking dog who caught the car, was invited in, and curled up delightedly on the seat...."

From "Letterman’s departure is 15 years too late," by Kyle Smith.

I feel much the same way, and yet, we all get old. Dave was getting old and we were getting old. We could stick with him and grow old with him, get comfy on the car seat, or we could stop watching. Me, I stopped watching. But that doesn't mean Dave should have stopped at the point where he was no longer the Dave that meant so much to me. It was okay for him to make a long soft landing into old age, to become Dad. Nothing really that wrong with Dad. The culture needs its Dad too. I mean, I might not want to watch Dad nod at celebrities for an hour every night. But it's okay that he's there.

Did Letterman dilute his legacy by sticking around so long? It's not exactly dada and surreal to analyze things in those terms.