Borderlands is a cell shaded FPS RPG set in a post-apocalyptic-like planet. The game is being compared to Fallout 3, but unlike that game, this one's more action and less roleplaying.
The other thing that is said about this game is that it is "Diablo with guns". After playing it for a few hours, I agree. It's the sort of game that is not very deep, completely unrealistic and sometimes totally ridiculous, but you just can't stop playing it. You just can't stop opening every chest and cache because there might be a better gun or shield device out there. And it's really fun to try out the different types of guns, check out the different scopes and firepower.
The map areas are quite big. On some of the maps, you can spawn a vehicle and drive around, and it comes armed with a cannon or a high-powered machine gun. And you can use it to run over your enemies -- it's insta-death.
Creatures and bad guys do respawn but only after a reasonable amount of time has passed. They don't reappear the instant you turn your head (like in Farcry 2). Treasure containers do get refilled.
It is a beautiful game, too bad there's more than a few incidences of graphical glitches -- usually when you're looking at the area map or when a cut scene is playing. And it could really use a few more varieties of enemies per map.
And there's the long loading times when the game is loading up a save or a new area.
Despite the glaring flaws (which is a big pity), the game is fun, packed with tons of good action and is very addictive.