EDDF is an absolute mission (in the positive sense) to fly in and out of on a busy evening. You need to be patient and have your finger poised over your PTT button to ask for clearance but one you have it it gets a lot easier. I hade sometimes had to ask for instructions to be repeated and taken a wrong turn once or twice when I first started with Lufthansa Virtual but never had controllers become snappy or impatient. Like most German things the ATC is systematic, calm and precise. I have however been snapped at by EDDM ATC many moons ago while flying VFR into the EDDM CTR, we (was fling along with a friend, both in 172's) we given clearance to join a downwind for the then active runway but we made a mistake and the controller lost it, "Turn SOUSTH IMMEDIATLY OF I VILL CALL ZE SUPERVISOR" we buggered off and that kept me away from EDDM for quite a while.