It's been so long and the season 8 travesty so fresh that it's hard to remember lol.
I think the damage is that it's one large story that hinged on the ending sticking the landing and...well, it certainly didn't. Other shows that start to lose steam towards the end or hit ruts can have jumping off points where you can still look back fondly on them. The Simpsons will always have those first 8-10 seasons no matter how long it goes, the X-Files myth arc may have been unsatisfying but the show's true legacy is the stand alone episodes, Buffy has seasons 1-5 being a more or less complete story that you don't have to continue on from, etc.