Limitations Might Apply to Luxury Cars
Car rental companies usually apply driving/drop-off restrictions when driving in Middle-European, African, Asian and Middle-Eastern countries. Mainland EU is usually restriction free, setting aside limitations applying to luxury cars. See for example the Hertz help page on the topic:
Hertz vehicles cannot be driven into and/or dropped off in any African, Asian or Middle-East country nor in Albania, Armenia, Azerbaijan, Belarus, Bosnia-Herzegovina, Bulgaria, Croatia, Czech Republic, Estonia, Georgia, Greece, Hungary, Kazakhstan, Kyrgyzstan, Macedonia, Moldova, Montenegro, Poland, Romania, Russia, Serbia, Slovakia, Slovenia, Tajikistan, Turkey, Turkmenistan, Ukraine, Uzbekistan.
Hertz vehicles cannot be taken to and/or dropped off in the following islands: Balearic Islands, Canary Islands, Corsica and Sardinia.
Vehicles may be driven but not dropped off into Portugal.
Since you are departing from the Netherlands, in the case of Hertz, note that come of their luxury cars cannot be driven past the border:
Please note: Dream Collection Special Roadster (D6): Porsche Boxster and Dream Collection Special 2-3 Door Automatic (L6): Porsche Cayman cannot be taken across the borders of the Netherlands.
It is safe to assume that other rental agencies will operate similar policies.
Beware of the Environmental Zones
More importantly in my opinion is that you should be aware of the environmental zones (Umweltzonen), which are set-up in most of the cities in Germany. Polluting vehicles, and vehicles without a green vignette (Umwelt Plakette) cannot drive into selected areas of the cities, and will be fined if caught. For more information see the dedicated TUV webpage (in English). Here is a TUV webpage detailing the list of cities where the vignette is needed.
Please note that rental cars are not exempt from this regulation, as per this question on TSE. Indeed Hertz knows, and mentions this in the afore-mentioned page:
*Please refer to "Environmental zones" in the German Rental Qualifications & Requirements if you intend to drive to or drop the vehicle in Germany.
However, as it turns out, Hertz cars rented outside of Germany do not carry the green vignette. Quoting from the Hertz help page on the topic:
All Hertz cars from Germany and Switzerland carry this stickers, however, Hertz cars rented outside Germany and Switzerland and driven into this two countries do not carry a sticker.
Therefore, Hertz customers renting outside Germany and wishing to drive into Germany and Switzerland and who enter a restricted zone, may be subject to the €40.00 fine.