Okay,
I can comment on the area around Bodensee (Lake Constance) and the region south of Munich. Not sure where you start and end the route and whether this is only part of your holiday trip but I would definitely recommend going to Salzburg for at least a few hours. It would be a shame, being so close to it, to not make a visit. Since you might not be allowed to take the car across the border and since the centre of Salzburg has a challenging parking situation, I would consider taking a train across the border and into the city. As far as I remember, there is also a train going from Munich to Salzburg in little time.
As others have said, I would take into account some places to enjoy the car on the Autobahn. The route to Salzburg can be quite crowded, depending on the time of day. If you take that one, use it at a rather uncommon time of day to enjoy it. The Autobahn from Munich to Garmisch is only a two-lane road (in each direction of course) but less crowded, the one to Salzburg usually three lanes wide.
I have visited the region east of Garmisch a few times and it is indeed a lovely area. I have attached some pictures of it below. It looks like a big trip but the distances are fairly small, if you are driving a fast car and have little traffic you can get through there rather easily. Apart from the major tourist spots such as Garmisch or Tegernsee you should face little traffic. At least that was my experience on all of these trips. If you exit the Autobahn towards Tegernsee you might face a long cue of cars, especially on weekends. Compared to the mountain region further South I have only experienced few motorhomes and caravans on this route.
Some recommendations along the way:
Kochel:
If you are interested in art, the Franz Marc Museum might be worth a visit. It features some beautiful architecture as well.
Garmisch:
The town itself does not appear too interesting to me but the trip to the Zugspitze might be interesting for you.#
Neuschwanstein:
Judging by the route, you will pass by Neuschwanstein and should pay a visit.
Lindau / Bodensee (Lake Constance):
As I have commented on Aaron´s trip already the lake itself is very beautiful, one can take a ferry across the lake from Meersburg to Konstanz and continue to the Rhinefalls in Schaffhausen, which are on Swiss territory.
Fischbachau:
Spitzingsee:
Walchensee:
Thiersee (Austria):
). It would be perfect if someone have done this rout before. What should I know about the rout? Interesting places? I don't want to miss something....Will be appreciate for any advice 
