One of the greatest things about the Borderlands franchise is that it literally takes at least 100 hours to reach the max level, and afterwards there are still ways to keep leveling, and if that's your cup of tea then you'll definitely be happy to go back and do it again on a harder difficulty.
However, despite Destiny having similarities to Borderlands in terms of world exploration and weapon looting, the leveling system will be entirely different. In fact, it will be entirely possible in Destiny to reach the max level cap within just a few hours of gameplay.
It's important to realize right away that although the level cap can be hit pretty quickly, the game will certainly not be over once the cap is reached. Instead, players will be able to put more focus into other aspects of the game, such as weapon upgrades and locating great loot.
Bungie's idea behind this is that they want to be able to offer players a level playing field as quickly as possible. In MMO's, joining friends can often be a frustrating procedure - if you start a new MMO, it would take dozens to hundreds of hours of leveling before you can even start to enjoy playing with your level capped friends.
In Destiny, this issue won't be apparent because the level cap will be reached early on, and once it has been reached, the biggest thing players will be working towards is finding better gear.
Destiny will be released this September, and a Beta should be available to those who pre-ordered some time this summer.