I call it P^3BL--passionate, personal PBL.
Passionate means there's something present in the project that the students put their heart into. They care about it and the expression is apparent to anyone who sees the project or presentation.
As an example, the teacher's at my son's school made a new requirement for science fair projects this year. Students had to base the project on something they were passionate about. It made an amazing difference on the variety of projects that filled the gym. It was interesting seeing the creative ideas students explored. I also can attest that it was a lot easier getting my 13-year old to complete his own project this time around, even though the subject (computer programming) was a challenge for him.
Personal means there is at least some element of personal style present that no one else would have, or maybe could have, done quite that way. Personality and experiences come into the mix in fresh ways.
For this, I would point to my Smart Jams music video project we completed this year. In it, students wrote and performed songs and raps. I had groups decide who would do the vocal performances and the singers (and wannabe singers) quickly came to light. It was great hearing those students improvise their melodies. Music tastes, songs and who knows what else blended to form their personal styles. Songs were simple, but the uniqueness was magical. (The project needs some tweaking so all group members get a shot at such self-expression.)
Note that these are emphasized in planning and reflection. Students need to build them in. As a group they need to make sure each group member will have elements they can point to.
And in reflecting on the project afterward, students must point out the elements that fit these criteria. My hope is that they will also find some things (or others will point things out to them) that they didn't plan for or notice themselves.