I am already longtime in photography, but I have to admit I don't know how to read such a graph.
Can anybody give me a crashcourse? Point me to what I need to look for (bad or good).
There's a lot of information in an MTF curve, but it requires interpretation as well (which takes a bit of experience). It's more useful when comparing several options.
In general it shows you how much contrast is reduced as a function of spatial frequency (high frequency is fine detail, low frequency is overall contrast).
Some more background in addition to the Zeiss references:http://www.normankoren.com/Tutorials/MTF.html