The ending is, in NO WAY, SHAPE OR FORM, a copout. It's the end of one of the biggest plot and emotional throughlines in the whole trilogy. When will Gotham no longer need Batman? Will Bruce ever be able to let go of Batman and the past? Will Bruce ever get a chance at redemption and a real life?
From BB:
Rachel Dawes: But then I found out about your mask.
Bruce Wayne: Batman's just a symbol, Rachel.
Rachel Dawes: [Rachel touches Bruce's face] No, *this* is your mask. Your real face is the one that criminals now fear. The man I loved - the man who vanished - he never came back at all. But maybe he's still out there, somewhere. Maybe some day, when Gotham no longer needs Batman, I'll see him again.
From TDK:
Rachel Dawes: Dear Bruce. I need to be honest and clear. I'm going to marry Harvey Dent. I love him, and I want to spend the rest of my life with him. When I told you that if Gotham no longer needed Batman we could be together, I meant it. But now I'm sure the day won't come when *you* no longer need Batman. I hope it does; and if it does I will be there, but as your friend. I'm sorry to let you down. If you lose your faith in me, please keep your faith in people. Love, now and always, Rachel.
TDKR provided an incredible ending to all of this. That final Bruce/Alfred shot was the climax of the emotional core of the whole series. The catharsis.