I thought I wanted this for the longest time but...
It's not as good as the two part version!
1. The house of blue leaves fight sequence in color seems unfinished because a lot of the blood is clearly water, it was meant to be black and white. There are a few added shots that are great, but it's not worth it. The shot of Sophie getting her arm chopped off is cool too, but still not worth trading film versions.
2. The fantastic intro and title card to vol. 2 is dropped all together. This 4th wall breaking monologue is one of my favorite scenes in the movie. It's noir, clever, funny and is yet another love letter to classic cinema with the line 'what the movie advertisements referred to as 'a roaring rampage of revenge'". It's just sorely missed.
3. The shift from part one and two is not smooth. The cliffhanger reveal is not as powerful when you cut to another scene as oppose to the ending credits. Cutting from Bill at the hospital in japan to then visiting Bud in Texas is also very jarring. The reveals of things like Bills face, Beatrix's name etc also loose their impact.
4. The split between films sort of serves as an intermission if you want to watch them back to back and is perfect for casual viewers to watch over two days. With no breaks this film is not easy to watch for 4 straight hours, and it's my favorite Tarantino flick.
When I first heard about this version I wanted it to replace the individual films so bad. I don't dismiss long movies simply for being long. I love a good 3+ hour movie, Hateful 8 Roadshow was excellent and the 4 hour extended cut of return of the king is one of my favorite films, but this story works better in two distinct parts.
If you are a hardcore QT fan, I definitely recommend watching it at least once to see a early rough cut of the movie, as this was the original premiere version at cannes. If you are a more casual QT fan, you aren't missing much and have seen the better version.