Borderlands 2 > Borderlands
Borderlands 2 is a significant improvement on the first game. It takes everything from the first game that wasn't just right and made it just right. It improved on the gameplay, AI, and story. It now has a great story which the original didn't really have. The gameplay did stay pretty much the same but just had some better features. I also fought the skills are better this time and so are the characters.
The story this time is much better because the fantastic writing. The story starts with you choosing a character and meeting Claptrap. There is only Claptrap left because Handsome Jack had the rest of them killed off, but he failed to kill this one. You can also choose to play in either single player or 4 player co-op. The boss fights that occur are also a lot more fun, certainly the one with the Bullybong that took Claptrap's eye in the beginning. The gameplay is one of the best parts about the game. It works excellently with the many different weapons and skills avaliable.
The characters are a little better than the first game's characters in my opinion because of the more developed skills. The character that is the most unique is Zer0. He has a sword for melee attacks and has a skill tree that strongly features it. The characters from the first game also make cameos in the game.
Overall, Borderlands 2 is a great improvement on the first game. It has excellent gameplay, writing, characters, and weapons. I enjoyed playing it very much and think it really earned it's 5 stars.