There are some shows that, regardless of whether their decline in quality happened gradually or very suddenly towards the end, are ultimately saved by their series finale. For example, many believe <em>Parks and Recreation</em>'s finale saved it. I thought the show was stellar from start to finish, personally, but I agree that the finale is absolutely brilliant. I like the later seasons of <em>The Office</em>, but I agree they weren't as strong as the earlier installments, but the finale is undoubtedly one of the best sitcom episodes ever.
