Hi everyone, Can't say about how difficult admission is, since I'm sure it changed like someone mentioned already.
I can reiterate the recommendations of other people here about the universities: Munich LMU, Freiburg, Luebeck , Berlin Charite... and would add Muenster and Hannover... but I would really advise to check out your choices in person after gathering all the theoretical info before you decide.
The USMLEs: don't worry about that at all. Of course, German med school doesn't prepare you for it, but it's not a problem to prepare for it yourself with all the books and materials available. of course you should plan to ace those - but since it's totally up to you when you take them, that helps.
I would be more worried about passing the GERMAN exams - you must be fluent in German, esp. reading and understanding!!! If you're not, I honestly don't know how you could make it...?
One nice thing about German Med schools is that you have very long semester vacations during which you can travel and study, and nice is also that you can set up electives and externships pretty much around the world -Fiji anyone? (in most cases must be total self initiative in organization).
If you want to come back to the US though for residency you have to keep several things in mind: a lot of German med students set up their electives and externships in the field they want to go into: for example they do 3 months of ENT (or more) - but you have to approach this differently. For one thing to make sure you don't have problems with state licensure later (f.e. CA) you should make sure you have the minimum full 6 or 8 weeks in the "American Med School core subjects" (psych, ob/gyn, peds, family med)- Germany will have you do rotations in forensic medicine (excellent by the way), occupational medicine, derm, and ALL the subspecialties and allows you to weigh your fields of interest heavier if you like - this is not what most states are interested in for licensure at all.
The other thing is that you must organize some clinical time in the US - and apart from some schools that have set up exchange programs you are on your own with setting that up - and I have the feeling that more and more students from more and more corners of the world want to do externships in the us now, so there may be more and more competition for those.
... and finally, yes, you will be an img, and while German med schools have deservedly a good reputation (with emphasis on the pathophys and theory of everything like people mentioned already) it will be hard if you are competing with american grads for anyhow hard-to-get residency spots in competitive fields! (and again going through the Match will be total self initiative) So for this reason you must be very cautious and plan well when deciding NOT to go to med school in the US!
Good luck!