The problem I see with PBL is that it is highly facilitator- and peer-dependent. If you have great group members and facilitators that know what they're doing and do a modicum of planning, then the experience can be fun and informative. If that doesn't happen, though, it can be miserable - you spend time talking about things that are irrelevant, you have no idea what you actually were supposed to take away from the case/problem, and, if your team sucks, you may not even get much out of the experience due to poor preparation and limited teaching.
You could say the same thing about lectures, but the difference for me lies in the fact that PBL at most schools tends to be required. If it ends up being a waste of time and not effective, you're stuck. If lectures suck, you can generally just not go to them, unless your school has an attendance policy or something like that.