Personally its not the slowness that I mind so much. I spent a week in Japan and was never bothered by their train system times and whatnot.
The thing that really grinds my gears about BART is that every freaking time in their time table is +/- 5 minutes. I can't plan any sort of schedule around it to save my life, and thus I personally feel that I waste a ton of time waiting around for the next train. I never felt that in Japan. Every transfer and connection was exactly on time and there were plenty of trains where I was never sitting around waiting 20 minutes because I just missed the BART.
The thing that really grinds my gears about BART is that every freaking time in their time table is +/- 5 minutes. I can't plan any sort of schedule around it to save my life, and thus I personally feel that I waste a ton of time waiting around for the next train. I never felt that in Japan. Every transfer and connection was exactly on time and there were plenty of trains where I was never sitting around waiting 20 minutes because I just missed the BART.