Jackson's ending made no sense, read zero, to me in 2 viewings. It grates more every time I think about it.
Tolkein's ending makes sense in every detail. It is beautiful. It is tragic. And it reinforces the fact that the bad guys can win.
This is absolutely and utterly integral to the power of the series as a whole. To understand this you will need to track down Tolkein's essay On Monsters. Read it. Until you understand what principles Tolkein conciously based his seminal work on, you won't really understand where the ultimate power of the whole works from.
Jackson is undermining the second and particularly third movies. And when he is all done and you try watching the series as a whole, it won't be as strong as it should have been.
I know you disagree now and are likely to for a good while. Let's talk about it again in 3 years, shall we?
Cheers,
Ben