I've listened to about a third of the series so far, and it varies widely from episode to episode, depending on the quality of the writer more than anything else. It's weird listening to a corny '50s whitewash being laid over it, but occasionally the real Archie or Wolfe will peek out from under all the treacle. They keep trying to find a formula, a catchphrase, anything to make it fit the mold of their sound-bite sensibility, but Nero Wolfe just doesn't work that way, and you can tell they are struggling with that.
There's also a rather lame recurring conceit of Wolfe always sleeping at his desk and being grouchy at Archie waking him up to take a case -- exactly the kind of thing that makes the '50s seem so square in retrospect, but probably what some producer thought was a swell gag. But when there's a good writer on the case, as I say, you can see the real characters make an appearance, such as Wolfe objecting to "superfluous interrogation" or Archie commenting that there hasn't been a man-eating tiger sighted on the New York freeway for nearly a year.
So, mostly mediocre with an occasional gem, is what the overall impression is so far. Worth listening to if you're a Nero Wolfe or a Sidney Greenstreet fan. As both, I shall follow it through to the bitter end, I suspect!