I want to preface my Redux comments by reminding you guys that this film is currently my #1 of all time. I've seen both versions in the theatre, own both DVDs, read Conrad's source material, seen Hearts of Darkness, and am currently reading a book about the production of the film.
I understand why some have a problem with Redux. It probably doesn't flow as well as the theatrical version, and not all the new scenes seem integral to the story. However, the film is episodic in nature anyway--it goes from set piece to set piece, and I'm not convinced that adding a couple more in really detracts from the tone and/or structure of the original.
Another common complaint is that regardless of how well the French Plantation section is written and shot, it's a huge detour at an important part of the film. Again, I disagree. Half the fucking story is a detour from the mission. Do Lung Bridge probably wouldn't seem to serve much of a purpose had it been dropped in as a new scene, as it's more psychedelic and out-there than anything else in the film. But the reality of the war is that this kind of shit was happening, and the French expatriates are as real as anything else in the film. The dinner argument provides a much more substantial political context for what's going on, and the love scene gives us another shade of Willard, who we don't get to know nearly as well as we do Kurtz in the theatrical version. Clean's funeral is so well-done and is a nice bit of closure.
The bottom line is that I love this film, everything about it, and to me the Redux just gives me more of that magic behind and in front of the camera. I doubt I'll ever watch the other version again.