I debated whether or not to reply to these questions or not, but since nobody else has - here goes!
This trip can be an outstanding one. My husband and I have taken it twice, so you know we are sometime happy campers. The first time we went was in 2001, shortly after 9/11. That trip was absolutely outstanding - excellent guide, well spaced itinerary, good hotels and so on. We did the "same" trip in 2011, and would say it was only so-so. The itinerary was a bit different, the guide was basically inexperienced, the driver excellent (but had never driven this particular tour before and we wasted quite a bit of time as a result) and so on. We also happened to have a truly elderly bus. We felt that the guide, although enthusiastic, didn't has the knowledge to get the best local guides when she called ahead, and just didn't add much to the bare itinerary. That said, we aren't really sorry to have gone again, because we loved the areas and cities visited and had a chance to see them again.
Specifically, the Berlin extension was problematic in our judgment. Berlin is a great city, and no matter how one sees it, that's basically fine. But -- our last tour spent three days doing the sightseeing stuff one does, then, when the main tour came to join us, we had our "orientation" tour while en route to the train for Warsaw. Fine, for the main tour only folks, but a waste of time for the pre-trip group, we thought. Some people didn't like the Berlin hotel, as it's location is a rather long walk from sights. We thought it was okay.
One thought - nothing directly to do with GCT. We happened to arrive during the Easter holiday which, in Europe, tends to be a ten day or so event, thus adding lots and lots of people to all the cities and, of course, sites such as Auschwitz.
I know you may think we just should have let the memories of our first trip rest in peace, but we have taken other trips more than once and had wonderful, if different, experiences. So -hope you enjoy whatever you choose to do.