Well, my wife and nephew spoiled the end for me as they went opening night and I couldn't go till the next evening. That was horrible, as I had avoided spoiler up that point.
My reaction was much like Rusty Cage's though. I was on a true emotional high, after seeing the respect and dignity that Nolan and Goyer had treated the Batman mythos with, then getting that confirmation that Joker would indeed appear on screen in the next three years. And then when Gordon apologizes for never having said thank you and Batman telling him "And you'll never have to", then diving off the rooftop. Ooh, damn, that sent chills all over my body. Soooooooo badass.
The theater was buzzing. Big time. It was much like the magic trick scene with Joker in TDK. You could just feel the electricity in the audience and all of those nearly inaudible expressions of excitement amongst the movie goers came together to create a really awesome buzz. God, it was just great. Thank you Mr. Nolan.
I started obsessing over possible Joker characterizations immediately and dived nosefirst into rumorville as soon as I got back home. I've been a spoiler junkie ever since.