As @Ian Cooke said,
The weakest link of PCI DSS is the availability; there is no reference in the whole standard. No availability, no business continuity or disaster recovery.
PCI DSS will give you enough details to implement technical procedures, controls and processes but the approach is not risk-based. (compliance).
It's a good starting point, but then your risk assessment will tell you what do you need to protect your business/information.
Does the standard provide assurance?Well, it depends on the business/information that you want to protect. Again for sure provide enough assurance for Confidentiality and Integrity. Don't forget this is a standard to protect Credit Card information.
Does PCI DSS cover all the IT processes?
ISO 27001 has a holistic approach and cover at a high level all the processes to protect information but is not detailed as PCI DSS so; you can map PCI DSS to ISO 27001 and have an idea of what is missing and what you need. Out there is plenty of articles and documents.Finally, have a look at the Verizon PCI compliance report. This will give you an idea of the challenges for implementing the PCI DSS requirements in business.