It's not that I hated the original endings, it's just that it changed a lot of established rules the franchise was running on in a very short timeframe. They failed to really back any of it up with justifications as to why what I was watching on screen was happening, and how I affected anything beyond choosing a different color and making some minor changes in who was coming out of the Normandy and what shape they were in.
By simply adding context to the original endings, they are improved significantly. I think that by taking the time to explain what was going on, and why you were seeing what you're seeing, the DLC accomplishes the task of bringing closure to the Mass Effect universe. That's not to say I find everything about it perfect. The final confrontation with the Illusive Man still makes me make a decision that goes against how I played my Shepard simply because I didn't talk to him in a certain way in one of our conversations. There were problems with my romantic choice feeling a bit insignificant by the time the game was through. However, the fact that I can actually see how my final choice affects the galaxy at large helps add a lot of emotion and closure to what was previously feelings of confusion and disappointment. Also, I didn't hear anything about Mass Effect relays blowing up, so unless I went deaf when it was mentioned, that was a smart move.
Overall, the DLC is worthwhile for the simple fact that it is a better ending thematically. I'm sure there are fair points as to where the DLC falls flat, but for me, it is a success. I just wish that we could've had this originally and avoid all the hoopla to begin with.