In a nutshell it wasn't a very "Disney" park. There were hardly any quality darkrides. For example, Superstar Limo was changed very quickly b/c it was viewed as a bad attraciton. There were no bigtime Disney E-ticket rides.
Even California Screamin' while a decent ride isn't themed in the true Disney sense. It's essentially an off the shelf roller coaster. Tower of Terror was added to get bodies into the park but it was an inferior version of WDW's. A Bug's Land was built barely a year after the park opened b/c there was very little for kids to do. The first year attendance was way below what was predicted. There really aren't a shortage of reason for "why so many hatin' on this park" prior to the recent re-do.
I think it can absolutely be considered a failure prior to the re-do. Disney decided to invest a billion dollars to change the park when it was barely five years old. As well, they physically changed the appearance of the entrance to the park and re-didcated the park 11 years after it opened.