We did a tour of the Bremen facility when picking up our new CLK in '07. Started with a short film about MB history, followed by being bussed to the SLK and finally CLK production lines.
Yes, it is full of robots in the early stages of body construction but then each car is crawling with assembly workers when being fitted out. It is fascinating to walk along the overhead walkways looking down at the assembly lines. We obviously had a good reason to go to the factory anyway and I wasn't too sure my wife would enjoy the tour, but even she thought it interesting. The chap who took our tour is a very amusing Irish fella who's lived in Bremen for many years, so would be a bonus if you got him.
Bremen itself is worth a walk round when you've finished the factory tour.
Oh and, not surprisingly, cameras definitely not allowed in the factory.