Well it's two things, mainly.
For one, most dubs still suck. I know Cowboy Bebop, Samurai Champloo, Fooly Cooly, and a few others have good voice acting, but the absolute majority of dubs are still horribly acted. Naruto's dub makes me want to cut my ears off. Anime like Outlaw Star screw up by trying to make some of the voices (namely Melfina) try too hard to sound like the Japanese voices: the fact is, the inflection and tone of Japanese speech and characters almost always sounds like crap when inserted in English dialogue. There are many common mistakes (and just bad voice actors) that contribute to this, and the fact remains that the vast majority of dubs absolutely suck.
The second most common issue is translation and pronunciation. In many cases, the translation of the dubs fails miserably where the subs succeed. Take Final Fantasy VII: Advent Children for example. Cloud spends the movie, and the two years preceding it, unable to forgive himself for Aerith's death. He's dragging the emotional burden of his guilt the entire time. In a pivotal scene, Tifa accuses him of this simply by saying twice a Japanese word that, in the culture, means that one is dragging something. But rather than communicating that, the translators for the dub had her say, "Dilly-dally-shilly-shally." Um... what? Unless you're watching Advent Children Complete, which released years after the original, there is no real explanation in the movie for exactly why Cloud is having such problems, and this pivotal scene where Cloud understands that he is dragging an emotional burden replaces the most important word of the entire movie to "DIlly-dally-shilly-shally?" Dilly-dallying doesn't even mean anything close to "dragging" in the first place! I missed the entire point of that film until I saw Advent Children Complete with subtitles, all because the translators failed immensely. To use another example, Orphen (an anime that actually has pretty good English voice acting) had a much more complex story that was dumbed down in the English version by nothing more than a bad translation. The villain had layers of character development completely stripped away, resulting in a more simple story than was originally intended. Even the classics of your childhood: remember the first Pokemon film? The one about Mewtwo? Originally, Mewtwo was confused, and his motivations were rather complex in their lack of understanding, and this was communicated throughout the film. In the English dub, he is pretty much just a purely evil guy who wants nothing more than revenge, and any complexity of thought or confusion on his part comes out only in the end, during the monologue about peace and love (which, by the way, was much more pronounced and melodramatic than the original; and when we take something Japanese and make it more melodramatic, you know something is very, very wrong).
Beyond that, too many dubs change some of the terms and such that really should be the same. To use Naruto as another example (dang, was that show badly dubbed), they translated many things that should have stayed the same. For instance, the name of the village, Konoha. It means "leaf," and was translated as such. However, most subs still leave it as "Konoha." Why? Because names like that are much more mysterious and fitting to a fictional fantasy world than "Leaf Village." Translating it exactly in that case just sounds stupid: it's true that most of the ninja villages in that manga/anime are named after elemental entities, but that is caught on through the rest of it. Same with Naruto's techniques. Kage Bunshin no Jutsu makes for a much more mysterious, magical feel than the Shadow Clone Technique. The translators went too far.
As for pronunciation, this is just horrifying. Japanese has different translation patterns than English; different syllables will be stressed, vowels will often be pronounced differently... as a result, names often have a different sound. But many dubs completely disregard this, either changing the names to sound more American or simply pronouncing them in ways that simply sound stupid. A recent example would be the dubbing of Clannad (a brilliant show that I guarantee will make you cry, no matter who you are). It was a mostly decent dub, but the names sounded terrible. One character is named Nagisa, which, in Japanese, is pronounced NA-gi-sa. In the English dub, everyone said Na GEE-sa. Another character, Okazaki, should be pronounced O-KA-za-ki. Everyone in the dub calls him "O-ka-ZA-ki." Try saying these out loud: they sound absolutely ridiculous. Similar travesties happened in Digimon Tamers: for example, the main character, Takato, rather than being said TA-ka-to, is referred to as Ta-KA-to. Shikamaru, from Naruto, rather than being called Shi-KA-ma-ru, is pronounced Shi-ka-MA-ru. Rather than having names that, while definitely not American, at least sound foreign, we have crap that just sounds stupid.
I would also like to point out a much more rare, but still infuriating practice: soundtrack changes. My personal favorite example is Digimon Tamers, which actually had a great soundtrack and some really awesome J-rock and J-pop. The dub changed that. They did not use a single track from the original music, and instead had a musical score that may as well have been taken directly from a random royalty-free music website. Even the opening and closing themes changed...
When I saw the English dub after loving the subbed version of Tamers, I was horrified.
The fact is, most anime dubs are terrible, because the voice actors suck, the translation screws with the story, and/or the pronunciations just sound terrible. There are exceptions, and I will not judge someone simply because they watch dubbed anime. But I prefer subs in almost every situation, simply because I have very rarely seen a good dub.
For one, most dubs still suck. I know Cowboy Bebop, Samurai Champloo, Fooly Cooly, and a few others have good voice acting, but the absolute majority of dubs are still horribly acted. Naruto's dub makes me want to cut my ears off. Anime like Outlaw Star screw up by trying to make some of the voices (namely Melfina) try too hard to sound like the Japanese voices: the fact is, the inflection and tone of Japanese speech and characters almost always sounds like crap when inserted in English dialogue. There are many common mistakes (and just bad voice actors) that contribute to this, and the fact remains that the vast majority of dubs absolutely suck.
The second most common issue is translation and pronunciation. In many cases, the translation of the dubs fails miserably where the subs succeed. Take Final Fantasy VII: Advent Children for example. Cloud spends the movie, and the two years preceding it, unable to forgive himself for Aerith's death. He's dragging the emotional burden of his guilt the entire time. In a pivotal scene, Tifa accuses him of this simply by saying twice a Japanese word that, in the culture, means that one is dragging something. But rather than communicating that, the translators for the dub had her say, "Dilly-dally-shilly-shally." Um... what? Unless you're watching Advent Children Complete, which released years after the original, there is no real explanation in the movie for exactly why Cloud is having such problems, and this pivotal scene where Cloud understands that he is dragging an emotional burden replaces the most important word of the entire movie to "DIlly-dally-shilly-shally?" Dilly-dallying doesn't even mean anything close to "dragging" in the first place! I missed the entire point of that film until I saw Advent Children Complete with subtitles, all because the translators failed immensely. To use another example, Orphen (an anime that actually has pretty good English voice acting) had a much more complex story that was dumbed down in the English version by nothing more than a bad translation. The villain had layers of character development completely stripped away, resulting in a more simple story than was originally intended. Even the classics of your childhood: remember the first Pokemon film? The one about Mewtwo? Originally, Mewtwo was confused, and his motivations were rather complex in their lack of understanding, and this was communicated throughout the film. In the English dub, he is pretty much just a purely evil guy who wants nothing more than revenge, and any complexity of thought or confusion on his part comes out only in the end, during the monologue about peace and love (which, by the way, was much more pronounced and melodramatic than the original; and when we take something Japanese and make it more melodramatic, you know something is very, very wrong).
Beyond that, too many dubs change some of the terms and such that really should be the same. To use Naruto as another example (dang, was that show badly dubbed), they translated many things that should have stayed the same. For instance, the name of the village, Konoha. It means "leaf," and was translated as such. However, most subs still leave it as "Konoha." Why? Because names like that are much more mysterious and fitting to a fictional fantasy world than "Leaf Village." Translating it exactly in that case just sounds stupid: it's true that most of the ninja villages in that manga/anime are named after elemental entities, but that is caught on through the rest of it. Same with Naruto's techniques. Kage Bunshin no Jutsu makes for a much more mysterious, magical feel than the Shadow Clone Technique. The translators went too far.
As for pronunciation, this is just horrifying. Japanese has different translation patterns than English; different syllables will be stressed, vowels will often be pronounced differently... as a result, names often have a different sound. But many dubs completely disregard this, either changing the names to sound more American or simply pronouncing them in ways that simply sound stupid. A recent example would be the dubbing of Clannad (a brilliant show that I guarantee will make you cry, no matter who you are). It was a mostly decent dub, but the names sounded terrible. One character is named Nagisa, which, in Japanese, is pronounced NA-gi-sa. In the English dub, everyone said Na GEE-sa. Another character, Okazaki, should be pronounced O-KA-za-ki. Everyone in the dub calls him "O-ka-ZA-ki." Try saying these out loud: they sound absolutely ridiculous. Similar travesties happened in Digimon Tamers: for example, the main character, Takato, rather than being said TA-ka-to, is referred to as Ta-KA-to. Shikamaru, from Naruto, rather than being called Shi-KA-ma-ru, is pronounced Shi-ka-MA-ru. Rather than having names that, while definitely not American, at least sound foreign, we have crap that just sounds stupid.
I would also like to point out a much more rare, but still infuriating practice: soundtrack changes. My personal favorite example is Digimon Tamers, which actually had a great soundtrack and some really awesome J-rock and J-pop. The dub changed that. They did not use a single track from the original music, and instead had a musical score that may as well have been taken directly from a random royalty-free music website. Even the opening and closing themes changed...
When I saw the English dub after loving the subbed version of Tamers, I was horrified.
The fact is, most anime dubs are terrible, because the voice actors suck, the translation screws with the story, and/or the pronunciations just sound terrible. There are exceptions, and I will not judge someone simply because they watch dubbed anime. But I prefer subs in almost every situation, simply because I have very rarely seen a good dub.
