I'm leaving for Berlin on Feb. 11 to start doing exactly this. This is great.
Also, if you go to Checkpoint Charlie, the Museum there is pretty good, and big, but during peak hours it is extremely crowded and this detracts from the experience. Worth trying to go in off hours for that one.
Also the DDR Museum is really great, as is the Berlin City Museum. Especially if you've an interest in the soviet era.