Borderlands is the newest release from Gearbox and 2K Games that admirably combines RPGish aspects with FPS gameplay mechanics. The result is an addictive game with mid-range replayability. The most fun you will have playing Borderlands is with your friends via co-op play. PvP is available, but it is so poorly balanced that you won't really want to waste your time, unless you make up rules such that the Hunter class can't use his bird and the Siren can't use her phase ability, etc.
The story for Borderlands starts you out on a bus, being driven to your first quest hub, given a short tutorial and thrust directly into combat. The first thing you notice is that instead of your aim and weapons being inhibited by your low level, your shots actually go where you aim and you are deadly accurate. It turns out, you are only inhibited by the level of your weapons and their measly 9 damage per shot. With enough time, however, you find some truly unique items including shotguns that fire rockets, automatic pistols that set your target on fire and other fun weapons.
Unfortunately, the itemization within Borderlands does not reach the level of most RPGs, seeing as you have far less than the usual head/chest/hands/feet/wrist/neck/fingers etc. slots to fill and the "talent trees", while useful, aren't really gamechanging though they do offer some uniqueness with respect to play style. For example, speccing into the Hunter's special ability will increase the damage done by quite a bit and will allow you to use it far more often. So if you like the special ability, those talents will be useful. If you're like me and just prefer to use your twitch skills to snipe people from afar, the other portions of the tree will be more useful.
Borderlands offers 4 classes which are roughly equivalent to what you would expect. The Hunter class fills the Sniper role, the Brick class fills the melee role, Soldier is the hybrid who has good healing and offensive capabilities and the Siren class which seems to be played best as purely offensive.
All in all, Borderlands offers the best combination of RPGish and FPSish gameplay mechanics in any game to date. If you like FPS shooters, Borderlands is a pretty good buy. If you like RPGs and FPS shooters, Borderlands is a pretty good buy. If you like RPGs and FPS shooters and have a couple friends who would play the game with you, Borderlands is a must have.