Mikey Neumann, creative director at Gearbox, has said that even though the level cap for Borderlands is 50, you can probably beat the game at level 31 or 35.
On top of that, the game allows for a “single-player plus” mode once beaten, where you can replay the game, ascend to level 50, and get the best weapons out there.
“The level cap is 50, but you beat the game around 31 or 35, somewhere around there,” Neumann told MTV. “Then you can restart the game and do New Game Plus where everything’s 35 to 50 on the second play-through.
“[There's] more rare enemies, too. The Badasses and the Brutes and stuff like that, which you don’t see as much of in the first. You see them a lot more in the second playthrough. It’s definitely harder.”
As far as length goes, Neumann says that going by his own playthroughs, it takes about 100 hours to finish the game the first time through. More should you go for a second round.
“I just have my own gauge. I’ve maxed out twice, gotten to level 50 twice,” he said. “It took me about 100 hours. More the second time, actually, and that was to find every single little mission. I wanted to do everything.”