Okay... this is going to be long so bare with me, because this is important and I promise I won't spam you guys again after I say this, haha. I feel like people are getting annoyed by me...
To me, the retired for 8 years is perfect.
It's perfect.
I don't know why people have a problem with it. People need to expand their mind.
"I don't see how he can be retired for 8 years, return and then not be Batman again and then come back to beat Bane and then retire again!!"
Think about it. The man is retired because it is the right thing to do, because he believes HE is responsible for all those deaths and because the police HAVE to chase him. Batman is the last "villain" in Gotham so he "disappears" as if the cops ran him off, giving Gotham the victory it needed with the death of Dent. It was a spontaneous Plan B.
Now, Batman is stuck retired. Earlier in TDK he wanted to retire anyway, but couldn't. Now, it's like a "be careful what you wish for" situation. Bruce has locked Batman away underneath Wayne Manor and knows he can't be Batman but wants it...wants it SO bad. Because despite his presence creating criminals like the Joker (escalation), Bruce NEEDS Batman. This is why he is "frozen in time" as Nolan put it. He is stuck in the place he was at the end of TDK.
So, finally, after Bruce is forced to bring Batman back at the hands of Gotham's greatest threat yet, as soon as Bruce finally decides, "Alright, damnit, I'm back and I'm going to destroy this monster, he's gone too far", he gets the hell kicked out of him.
How damaging can you imagine that is?! It's an amazing storyline. I feel it is even better than Knightfall.
Now, Bruce has to try and come back all over again. But, he's locked away. Forced to still be Bruce Wayne.
Do you see how genius that is? First, Bruce Wayne himself forced Batman away, then, Bane forces Batman away.
This makes for an ultimate rise and for Batman to reclaim his place as the hero of Gotham.
After TDK, Gotham is in peace..but it is a fake piece. After Bane almost crumbles Gotham to rubble and Batman finally beats him... Gotham will grow back and have REAL peace and Batman will no longer be just a masked vigilante, hated by half the city and hunted by cops. He'll be a legend. Then he can truly quit.
This brings this quote home from ALL THE WAY back in Batman Begins:
"No one can save Gotham. When a forest grows too wild, a purging fire is inevitable and natural. Tomorrow the world will watch in horror as its greatest city tears itself apart through fear. The movement back to harmony will be unstoppable this time."
That's another part of the genius of the story...
At the end of TDKR Batman will truly save Gotham and bring it to harmony after it tears itself apart. Only not in the corrupt way the L.O.S. was going to do it. Batman does it in his own way.
(Just like he refused to kill that criminal all the way back in Batman Begins)
FULL CIRCLE.
...RISE.