Well, yeah, the LotR movies are orders of magnitude better than the Hobbit ones (especially DoS). I would say that the LotR movies are probably the best adventure/blockbuster movies out there, taken on their own merits. I just don't think they live up to their enormous potential, which they could have if they'd been truer to the books in certain regards. Also, note that I'm not saying "They changed it, therefore it sucks;" I'm saying "A lot of the changes they made suck." To adapt something as ridiculously long and complex as LotR into a movie, you're gonna have to make changes. And many of the changes they made are fine or don't matter. For instance, I don't give a darn about the old debate about whether or not the Balrog should have wings; it looks cool, and doesn't really undermine anything.
Oh, yeah, the transformation into such a wretched thing is important; it shows, in multiple ways, how evil the Ring is. But I think the split-personalities thing is a huge oversimplification of his soul. In the book, he seems to vacillate between wanting to redeem himself and still being evil. It's clearly a fight with his inner demons, caused by the Ring. But in the movies, his split personalities get rid of 90% of that. Instead of struggling constantly with temptation, he just tells his bad side to go away. Then later he tells his bad side to come back, and he's bad from that point onward. There's no depth to it; he's a cartoon version of himself (and I'm not referring to the CGI).
Honestly, I don't remember enough of either the book or the movie version to comment much more. It's been way too long.
Yeah, it as a good, even great, battle scene; I just don't think it belongs in LotR.
That is a cool scene. Thinking about it more, though, they probably could have just written that whole subplot out, ala Tom Bombadil. It's not super-important.
The Ring definitely is a corrupting influence on Frodo, but at that point in the story he's not so far gone that he'll essentially betray his only real friend. (Well, only friend he wasn't cut off from.) That doesn't happen until he's inside Mount Doom. So, basically, Jackson showed how the Ring was changing Frodo by changing Frodo into a jerk. Completely messes up the character IMO. He's the Ring-bearer largely because he's innocent and can resist it more than anyone.
Thing is, they were hardly in the movie. They get maybe half an hour at most, probably not even that. It's good that they were in there, but the Hobbit-whimsicality was severely overshadowed by the rest of the movie.
Just to help my case: I don't really agree with him on this, but here's an article about Christopher Tolkien's (J.R.R.'s son and basically the greatest living Middle-earth expert) opinion on the movies that got me thinking more critically about them: http://www.worldcrunch.com/culture-society/my-father-039-s-quot-eviscerated-quot-work-son-of-hobbit-scribe-j.r.r.-tolkien-finally-speaks-out/hobbit-silmarillion-lord-of-rings/c3s10299/#.UMCVFpPjnfY