I think Japanese people put more emphasis on pronunciation than we do in English. For me, it's grammar. If I hear someone say "I go to the bathroom" instead of "I WILL go to the bathroom" with perfect pronunciation the red light goes off in my head a lot more than if someone places the accent in the wrong spot. If you place the accent in the wrong spot in Japanese, I feel like their red lights go off. Like, if you same tsuNAmi instead of TSUnami, it goes off big time for them. I feel like if your grammar is good, then I can understand you more. If you mispronounce something and the grammar is good, I can probably guess from context what you're talking about anyway. I guess pronunciation is important but what I'm trying to say is that when I listen to someone in any language, I'm MUUUUUUCCCH more sensitive to their grammar than pronunciation. Anytime they forget "will" or plurals or "the" or "a," I feel like it's the same thing for them when you have that gaijin accent.
This is why it's so hard to learn another language. Every language has its own standards and ideas for speaking well. In Japanese, you have to be succinct and efficient. In English, we prefer to be clear grammatically and leave little to be understood in context. If you think about it this way, the two are exactly opposite.
Japanese is concise.
English is precise.