The main aim of signing Ronaldo for Juventus was clearly to win the Champions league, which they didn’t achieve. I see this as the main reason why people claim Ronaldo wasn’t a good signing for Juventus. As well as him being one of the main reasons for Juventus’ economic issues.
The aim was mainly to flee from the spanish tax authority.
And no, it wasn’t a success. Juventus was multiple league champion and CL semi finalist for years. With Ronaldo they lost in the last 16 in the CL and didn’t even win their home league.