A lot of guys have good in-ring work doesn't change the fact that his last title reign turned me off of Smackdown for months.
It did for me as well, but let's look at context here. We can't even begin to talk about poorly booked title reigns when it comes to Jack Swagger, and ignore how Mysterio's reign was booked. It was absolutely horrid, and the bookers were absolutely out of their minds. Imagine if he had won the belt in mid-2009. His reign would have included his feuds with Chris Jericho, Batista, Dolph Ziggler, and CM Punk, along with matches against Jack Swagger and John Morrison. It would have been one of the best wrestling-oriented reigns in some time. Even people that are tired of Mysterio have to admit that his work has been off the charts for the last year-and-a-half. And, unlike many other wrestling-oriented "superstars," Mysterio is able to maintain a HUGE fanbase without the big promos over-the-top booking.