Originally Posted by Dr. Linus
To be fair, that's exactly where the book ended. In fact, the film has more of a climax than the book does, which doesn't have Boromir's death occur until the very beginning of The Two Towers.
It works fine in my view, provided you accept that in any opening act of a three-part story, the first part will only ever have an emotional climax rather than a plot-related one, and I think it's one heck of an emotional climax - Frodo and Sam's scene in the boat is one of the best of the trilogy IMO.
That's what my book-reading friends told me, which is when my view on the ending started to change. Seeing all three films together really is a joy to behold.