Any workflow orchestration horror stories?

I'm working for a company that has a number of manual tasks that we need to automate in order to successfully scale.

In doing some research for solutions I've stumbled into the world of workflow engines. These seems like they can solve the problems for us.

In a nutshell, my use case is: - submit a workunit into a queue - determine some logic that routes the work unit either to an automated system for completion or a manual system for review. - after a manual review pass it along to the automated system or reject it.

It seems like these systems are tailor made for this. I am however always chasing shiny new tech. Before I go further I'd like to know horror stories of people who have failed in implementing these or, after implementing realized it was overkill and should have just built it by hand.