I think what ruined the DR scene in X3 for me was that I knew it happened. For those who did not know **** about the movie, it must have been a great surprise. I myself, 1 or 2 years before X3 came out, used to suggest in other forums that there would be no better way to start an X-movie than having the X-Men in a huge action scene, and then in the end we found out it was the DR. It happened exactly how I used to picture, but as Angamb said, the character interactions and overall power displays were beyond poor. The scene didn't even have its own musical theme, just bits of the movie cut to rougly match the footage. Rogue and Colossus sucked hard, and it all seemed like a "Let's praise Wolverine" moment, unfortunately.
Once again, the fact I knew absolutely everything about the scene was a big factor. I clearly remember one woman on the cinema that, when she saw the Sentinel head falling, she said out loud "Oh My God!!!" and then after some silence, "Was it a real Sentinel?" to the person beside her. I could hear more surprise sounds after the room starts to disintegrate. I wish I felt that, and this is why I pray that I can be at least 80% spoiler free for the future movies...I know it will be hard, since I've already read a script review for Wolverine, but I'll try. Wolverine is not a movie I'm looking forward to watching on cinemas anyways. Unless I read spetacular reviews (which I doubt), or that some X-Men appears in it (which I also doubt), I'm waiting for the dvd...
In the end, I blame X2. If the movie wasn't so great, I surely wouldn't want to know everything about X3 like I did.