A boring wash, rinse, repeat adventure. Borderlands does what other games have already done much better.
The game boils down to being confronted with a wall of text giving you a quest, killing and or collecting to complete said quest, then returning for a reward and XP. There is no character development beyond physical and battle abilities, no true interaction with AI characters, and little reward in completing obscure quests other than gaining XP.
Weapons are one thing that slightly stands out, with different elemental abilities you can inflict pain onto your enemies in a variety of ways. However you'll constantly be checking dropped items from bodies to see if it's an upgrade from your current loadout. It becomes second nature to scour the ground for weapons, money, and ammunition so much that it really subtracts from the game. There isn't any thrill to finding something new other than letting you kill enemies slightly faster.
Other games have followed a similar style with much more success. Fallout allows for great character interaction and development. GTA/Read Dead Redemption rewards the player with cut scenes and story progression. But Borderlands had me dredging thru just trying to beat it for the sake of finishing it.