For those who study in the humanities, have I made a mistake in doing my Master's abroad? I'm an American student currently earning a Master's in American cultural studies in Germany. Why study American culture in Germany? Firstly, I wouldn't have been able to afford a U.S. Master's in this field, and secondly I'd like to learn/improve my German with the ultimate goal of (possibly) pursuing a PhD in comparative literature.

However, since classes have started here, I'm beginning to regret my decision for the following reasons:

A) classes are incredibly large, direct contact with professors is scant, and so, among the obvious academic disadvantages, I'm ultimately worried I won't be able to get good letters of rec.

B) even at the graduate level, many students don't take their studies seriously (probably because there isn't the pressure of student loans and because education is quite open here [a good thing])

C) classes are not as rigorous as they were in my B.A. literature program, and so I don't feel like I can grow as a researcher/scholar, which is my goal

Does anyone have a similar experience applying to American PhD programs after doing a Master's abroad? Should I just stick it out and try my best to befriend some professors and make the best of my time here?

At this point, I regret not applying directly to American PhD programs sans Master's degree since my undergraduate grades and professors were quite good.
Thanks in advance!
You may have made a mistake, but it isn't a fatal one. You need a path forward. 

First, your undergraduate professors can still have credence in writing recommendations, but you need to keep in contact with them so you aren't forgotten. They can probably give you advice now on your current situation. 

I assume that you are early in your European studies. Abandoning and starting over in a US doctoral program might be an option, though perhaps as last resort. 

The B) issue can, perhaps, help you with the A) issue. Professors might be a bit tired of lazy students and could possibly appreciate an approach from a student who wants to do more, both helping with the letters of recommendation issue and your C) problem. 

But, it won't work if you are passive. You need to take charge. If one of your current professors does something interesting, you could make an approach and offer to help in some way. This solves all the problems. But don't just "stick it out". Take charge.