In all fairness to dub quality (not excusing the often less then stellar actor performance though) it's very tricky to write a dub script that both matches the lip movements and makes sense.
Compare:
"Watashi wa e-ru desu"
to
"I am L"
The easiest English translation is a 3 syllable uttering, while the Japanese line is a 7-8 syllable one, depending on if L leaves out the "su" in desu (never watched Death note myself, so I'm not sure if he does or not)
That's just one sentence out of thousands that must both be translated and made to match lip movements, I give the script writers a lot of credit for the job they do. Now the voice actors are often terrible, but that's another issue all together.
My thoughts on dub/sub in general (was talking about avatar the last air bender, but I'm lazy so I'll just copy/pasta)
Quote (Myrddrall9 @ Jan 2 2013 10:29am)
As a cartoon it gets 9/10.
As an anime (watched by non-Japanese speakers, if it hypothetically was an anime and not an American cartoon) it looses a lot of its strength because of the language and cultural barriers. One of Avatar's greatest strengths is the snappy dialogue and Americanisms mixed in with Avatar's unique setting that makes it a hit. Unless you know a ton about Japanese culture and have a strong grasp of the language, many nuances are lost, and many jokes just don't make sense/aren't funny. Of course there are jokes and such that are universal or easily translated but just look at the English release of Sayonara Zetsubou Sensei. There were like 10 pages of notes in the back, explaining all the subtle references and uniquely Japanese humor.
The same goes for Avatar, when you watch the English version, you are getting the original; the creator's vision, without any stripping down (which is a inevitable process when something is dubbed into another language or even subtitled). IMO Avatar would be a less then stellar anime (again taken from the perspective of a non-native viewer, forgotten quickly. 5-6/10