Ppl who down-rate this game have never played the first game and usually make points that don't matter.
As for most of the negative player reviews,
these ppl have not even pointed out one valid claim nor have they even given the first game a chance.
There is too much to say, so I might as well make a list of what is different.
+NPCs actually walk around, talk more and feel more alive.
+Story is noticeably better than the first, whereas in the first, it felt nonexistent.
+UI is easier to navigate. (click a shield twice and it will replace the old, etc.)
+Quests/Missions actually give you a sense of what you are doing.(the quest givers tell you what is going on without you having to read a huge chunk of text).
+Environments and enemies are far more varied and diverse, whereas in Borderlands 1; it felt like it was all sand and caves(excluding Knoxx DLC, etc)
+Weapons are more diverse and each have a unique look,whereas in Borderlands 1, they all looked and felt the same with different colors.
+Sanctuary is much needed in this series. It serves as a safe haven with a Bar, Slot machines used for gambling, townspeople, an HQ with a bank vault, Claptrap's place for your amusement and transferring items between characters, actual Shops for Guns, and more!) while in Borderlands 1; New Haven was a garbage dump that was no larger than my own house with barely anything.
+Skill trees and action skills are more fun, effective, and have far more depth and are more diverse. (the Turret actually is useful!)
+Explosives(grenades, launchers) actually feel dangerous, instead of party poppers in the first.
+Customizable skins, heads that you UNLOCK during GAMEPLAY! unlike other games where you purchase skins through real money.
+Playing Solo isn't as dull(compared to the first), and does not feel as much of a "chore" even after long hours of play.
+more than 1 Playthru(gives veterans more of a challenge)
+Gun/Treasure chests are actually what they should be?: Treasure! they are not as common, and are not in every corner of every map.
+Money has more value! (i had $99999 in the first game and ammo was EVERYWHERE.) In BL2, ammo is more scarce and has more value.
+Trash guns do not drop after killing 2 enemies anymore! Less unneccesary trash loot, which is good!
+Snipers are snipers!