As for the quality of different translations, tones of paper can be written about that. I sometimes start to think that some translators don't fully understand the importance of their work in making readers able to appreciate the beauty of the author's language, or understanding the message that he wanted to communicate. I agree that there may be (and are) serious differences between various translations, but to my mind the age of translation is not the matter. Some older translations may seem incomprehensible to a modern reader; nevertheless, they can be simultaneously a perfect communication of the author's ideas, just described with old-fashioned vocabulary. More modern doesn't necessarily mean better. In some cases, old-fashioned language is even more justifiable and appriopriate, if the book was originally written in, let's say, 15th century. The usage of an old-fashioned words sounds more natural in knights' mouths.
I read most of the books in translation, so this matter deeply interests me. How angry I was when I came across an edition of my beloved "Ann of Green Gables" with grammatical mistakes, which made it totally unreadable!
By the way, a good translator may have a huge impact on how the book is viewed by people! In Poland, we have an absolutely perfect, old translations of two books for children: Winnie the Pooh by Irena Tuwim and Anne of Green Gables - don't know the name of a translator, though. Funny is, that Winnie is called there Jimmy, and Rachel Linde - Margaret. Nowadays, for instance when new Disney's films are released, Winnie is still reffered to as Jimmy, and Rachel as Margaret (with they real names sometimes being clearly heard in the background!), even though different translators write the texts!
Another digression: in some film, a word "hamlet" was translated (or rathet left without translating) as Hamlet = Prince of Denmark, instead of a "cottage". Which made no sense, of course.
