Tom Prete, do you think you could tell us about the education there and how it compares to the university in your native country?
Do you have any specific question?
During my year at Keio I took many lectures taught in English, Japanese for foreigners and only 2 regular lectures in Japanese (politics and economics). So please bear in mind that I have only limited knowledge about regular courses taught in Japanese and I don't know anything about master courses. Also, I heared that things are very different at SFC (shonan fujisawa campus).
Compared to my home university (which is in western europe, please ignore my flag) the difficulty was lower. At Keio it is easy to get good marks as long as you a) attend (they check attenance) and b) hand in the stuff you're supposed to (quality isn't that important it seems). Lectures in Japanese might be tough if you have less than an 1kyu, but its doable with a good 2kyu. Depending on the lecture you have to hand in essays or take exams...that's when you'll need your language skills.
Lecture style varies a lot depending on the professor, subject, number of students, etc.
So generally speaking attendance and papers are much more important than at my home university where we don't need to show up and have 1 exam at the end of the term (most of the time). However, in my country, if you can't show, that you memorized and understood most of the stuff you'll fail or get a bad mark. At Keio you won't fail if you attended (even if you slept during class

) and as long as you hand in SOMETHING. That was my impression.