Europe is pretty much the hotspot for MIM, so good choice on narrowing down your geography.
If you are keen on pursuing a post-grad degree in Germany, ESMT is a good bet..like you say, it has shown a lot of potential and has risen up in the rankings this year. Also consider ESCP and WHU, which are more established, rankings-wise.
One very important criterion for selecting a particular B-school ( which many students miss out on when they are making their shortlist) is the post-MIM industry of choice. Have you considered which industry you'd like to enter, and whether Germany is a good long-term choice in terms of industry? If you have done this research, great!
On the other hand - if you haven't yet definitely settled on Germany, you may want to consider the top-10 list of MIM programs in Europe, and see if there are other schools that offer you a better fit.
1. St. Gallen, Switzerland
2. HEC, Paris
3. Essec, France
4. CEMS
5. Erasmus, Rotterdam
6. LBS, London
7. ESCP, Europe
8. WHU, Germany
9. Bocconi, Italy
10. IE, Spain