«Borderlands Complete»

I've finished Borderlands completely with a character now (a Siren). Gone through Playthrough 1 and 2. When I was doing Playthrough 2, I saved most of the sidequests for the unofficial Playthrough 2.5.

In Playthrough 2, you start the game over with your character and gear intact from the first Playthrough. The enemies are tougher and the "Badass" enemies are renamed to "BadMotha".

Once you've beat the main quest in Playthrough 2 and reload your saved game, you're in the unofficial Playthrough 2.5. In Playthrough 2.5, all enemies are between level 48 and 52. And "BadMotha" becomes "SuperBad". The maximum level for a player is 50, so it's common for enemies to be higher level than you are.

Now that I've completed every quest, the only thing left to do is collect rare weapons and search for secret locations and Easter Eggs¹ hidden in the game. Or start a different type of character. And there's always online play with other people.

^1: An Easter Egg in a game is not literally an egg (usually). It's just something hidden in the game. They usually require the player to go out of their way to discover.