The actor - who plays Jesse Pinkman - told Entertainment Weekly that new episodes of the AMC drama will be "much heavier".
"Walt's been going down this dark rabbit hole for a very long time," he explained. "And you see that he doesn't want to come out of it."
Paul added that meth manufacturer Walt (Bryan Cranston) is no longer motivated solely by money.
"It's about much, much, much more," he hinted. "And he's dealing with some inner demons that he's been fighting his whole life."
Breaking Bad creator Vince Gilligan recently told Digital Spy that he and his writing team are working to make the final episodes as "satisfying as possible".
"I will say, at the end of the day, we're gonna do our damnedest to make this thing end with a blast and end on a high note, in a way that will satisfy everyone," he said.
The fifth season of Breaking Bad will be divided into two parts, with the first eight episodes premiering on Sunday, July 15 at 10pm. The final eight will then follow on AMC in summer 2013.
> Breaking Bad: Laura Fraser to play major role
Watch the new trailer for Breaking Bad season five below: