Installation is (typically) a bit painful out of the box and requires expert help.
Following installation, initial projects require outside consulting expertise to be successful. Projects without importing BPM expertise tend to have much higher failure rates. Though individually the technologies involved are widely available and not complicated, combined and collectively BPM solutions require a flexible, creative, technical talent to help deliver. It takes time to learn the judgment and craft required.
The out-of-the-box UI controls (widgets) are not terribly inspiring- on desktop or mobile. Use of third party toolkits (e.g. Brazos) is recommended. Silver lining: those third party toolkits are quite good.
We use IBM BPM more to help our customers than to help ourselves. For our customers, IBM BPM has helped us dramatically reduce cycle time of previously manual processes, while increasing accuracy and customer satisfaction. However, it is difficult to get customers to go on record with ROI as they treat this as confidential/private information.
IBM BPM is enterprise software. It has some of the generic pros/cons of enterprise software, some of which didn't get covered in this review. It is increasingly available in the cloud - and increasingly supports mobile scenarios. In some ways it benefits from getting to the party late, and having cloud and mobile infrastructure so much easier to build upon.
It scales from small team interactions to business processes serving thousands of employees, as well as straight-through-processing needs that go well beyond. Of course, scale is always in the eye of the beholder, but IBM BPM does a good job of giving you all of the hooks, APIs, and data that you need to take on whatever scaling approaches you need to meet the load.