I have been flying JL for a few years now and have had little to complain out. While service may not be exemplary or memorable for me, it's competent, diligent and caring enough to make your flight pleasant and as trouble free as possible. A few things that do irk me is, and this is just me, that I find the food to be rather bland. Business Class menu has fair offerings but I find that dishes don't have much flavor and are also served just warm when hot is what should be what the dish should be served at (Western menu main course items), but nothing to do with cabin crew. My other issue, and this is par for the course for foreigners traveling to Japan, is their English is somewhere between basic and fluent, and this goes for both cabin crew and ground crew. If you have any issue that is beyond the parameters of the reasons why you may be engaging with the staff member, then it becomes a real struggle. I lost my earbud headphones in the lounge and trying to explain this and requesting if anyone had found them and turned them in was not exactly an easy process.
My expectation is that in today's day and age with increasing globalization and interconnected societies and economies, that JAL would at least place particular importance to English language speaking skills and make sure staff were as near fluent as one can be to manage and solve issues on their own.
I only came across one flight attendant on a JL flight, she was Japanese, who had a strong American accent and spoke impeccable English and was much more friendly and interactive compared to her peers. Turns out she spent a few years in California on a sports scholarship or something hence her language skills. I don't mind the lack of fluency as such but I just have to make sure I speak in a manner that will not confuse or lose them. Same goes for some of JAL's written material, lot's spelling and grammatical errors, but that is not unusual for a Japanese company which primarily works in Japanese. Other than that, crew are generally formal but relaxed and keep interactions with you to the necessary.
Finally, I saw my first male cabin attendant on a flight to JFK, was very pleasantly surprised, I thought the cabin crew for some reason was always all female.