1) Why is the New World Translation Bible so different from other versions?
That depends on which particular difference that concerns you.
a) Verb tense - the New World Translation conveys an "ongoing" verb tense for verbs that most modern English translations convey in a past tense. The appropriateness of using the past tense in these cases is, apparently, controversial.
b) "Jehovah" - though the NWT uses "Jehovah" to render the tetragrammaton, they *also* use "Jehovah" in passages in which they believe that the Father is meant, but where the tetragrammaton does *not* actually appear. All of these instances of altering the original language text to "Jehovah" are very well documented.
c) Translation bias - the NWT makes great efforts in translating the bible in a way that most strongly supports their existing doctrines. Thus, they frequently prefer the Septuagint (LXX) to the Masoretic Text (MT) in the "Hebrew Scriptures" - not in cases where the MT is unclear, but rather in cases where the LXX more obviously supports their doctrines. Similarly, the NWT translators are prone to choose less likely translations that support their doctrines rather than more likely translations which appear to undermine their doctrines. Note that this is *not* the same as mistranslation (although I feel that two passages demonstrating mistranslation have been presented to me and proven satisfactorily). Rather, it is reasonable translation directed by bias. Note: I also know of 2 passages in the New American Standard Bible where bias has clearly resulted in an alteration of the meaning of the text - so for me to identify 2 instances in the NWT is not extraordinary and does not mark that bible as profoundly faulty.
2) Gen 1:2
Here is a good example. This is what *I* would call a "stretch" on the part of the NWT. The adjective here can be properly translated "God's" - but "active force" is a very questionable translation, one of the few that I feel uneasy with in the NWT. This word can be translated "wind", "breath", "spirit", "ghost", etc. - but, as far as I know, there is no example of this word being translated in the unlikely manner "active force" outside of the NWT. An interesting note: the New Jerusalem Bible uses the phrase "divine wind" in this verse - which is, by comparison, a wholly reasonable and justifiable translation. The NWT translation of the phrase commonly rendered "holy spirit" as "God's active force" in every instance seems to go too far in degree of "unlikely" translation. If there were historic example of such a translation for this phrase, it would be much more palatable.
3) Jhn 1:1-2
The classic passage presented to me as an example of mistranslation on the part of the NWT - and which, to the best of my ability to determine, is *not* a mistranslation. Apparently, because of Greek syntax, the most literal translation is something like "the word was Divine" or "the word was Godly". However, "the word was God" is quite reasonable, and "the word was a god" is less likely but definitely not unreasonable. In other words, this is *not* a mistranslation - it is, rather, a less *likely* translation. Still, it is a justifiable translation - by that I mean, it could be correct, and it is not an example that someone can point to and say, "I can prove this is a mistranslation".