Picture world of warcraft style questing, diablo loot and character development, while playing a first person shooter and you have Borderlands. I played co-op split screen with a friend and solo mostly. Co-op is very fun and keeps you at it for hours. I would have to say one of the greatest spilt screen games I have come across. Playing solo can get a bit boring later on in the game because quests start feeling repetative. (run over here collect/and or kill this and return) Online play can be a bit difficult if you are grouping with randoms due to having to find someone around your level. Although, area matches are a fun break from quests. If you like FPS games and lots of inventory/character managment Borderlands is definitely worth trying out.
This is a game that I can already see myself playing for a long time. Some love it, some hate it, but I certainly would call this a great game. Many people say it gets repetitive and boring fast, but I don't agree. After a long day of work it feels good to be able to pop some heads and get rid of your stress. In this game, unlike most other RPG games, I actually find myself ENJOYING grinding for levels. It's like many Valve games. The story isn't meant to be the strong point of the game, the gameplay is.