The biggest disadvantage of bpel is the missing feature of human interaction integration. BPEL itself, according to the current standard WS-BPEL 2.0, is designed for fully automated processes only. But as real world projects show, most business processes have the need to do some activities non-automated - e.g. to get some decision from a real person. Therefore we have a whitepaper, BPEL4People, since several years now. Most vendors of bpel engines implemented custom solutions to handle human task stuff - like the BPEL4People whitepaper describes.
Now the scene is moving on: We will get a spec called WS-HT (Human Task), which describes a service interface for a human task workflow service, basically. Then we get WS-B4P (BPEL4People) which describes how to integrate WS-HT in WS-BPEL 2.0.
That's great news. So we have one more useful component for our SOA world.