The time that he was on about 3 or 4 different teams. Jason Aaron did a fantastic job with him, from most of his stuff that I read.
"Jumping the shark" is defined as a point where far-fetched events become novelty and quality declines. In Wolverine's case, that "far-fetched novelty" is more often than not his out of control healing factor. Back in the day, he was easily subdued, but then it got way amped up to where he was healing from nuclear ground zero in minutes. Quality has suffered because of this.
Overexposure is novelty, in itself. And there's zero question that the overexposure has lead to a decline in quality.