If you're not TOO focused on a very well developed RPG-game and could live with something more Gears Of War-ish, you can try Dark Void (buggy, and the story is a bit meh, but it's based on the Unreal engine just like ME and the gameplay is pretty adequate, plus the jetpack is awesome) or Vanquish (very fast-paced, takes the story a bit too seriously and has a few cheap boss fights, but definitely good for an adrenaline-filled night of gaming).
As far as action-RPG's go, the PS3 isn't exactly the best console. Demon's Souls is a rather well-made Action-RPG, but the story is very open-world and more in the vein of Oblivion, where you need to basically discover the story for yourself, and the difficulty level is insanely high.
Bioshock does have RPG elements and an extremely good story, though it's a first-person shooter. If you want squad-based action-RPG's, you really are mostly forced into Bioware games: DA:Origins, DA2, ME2. DA:Origins is a bit lacking on the PS3 though, the controls feel a bit stripped compared to the PC version.
If you're a fan of superheroes, Marvel Ultimate Alliance 2 is very close to being an RPG, it has elements very similar to older isometric dungeon crawlers, and the story is pretty well done for a comic book game. (And Deadpool is the most hilarious character in the history of the Marvel universe.)
If you are a patient gamer (This also would apply to Demon's Souls), you could try Sacred 2: Fallen Angel, though it does have more in common with MMO's than most action-RPG's. It's very similar to the games Champions of Norrath and Champions: Return to Arms, which themselves are somewhat like Diablo or Gauntlet.
And as everyone else has mentioned, Alpha Protocol, which is probably the best choice for an RPG game, as it lets you have free reign over almost every situation in ways many games could only fathom. All of the other games I've mentioned are more action-based than story-based (Aside from Bioware's games, obviously, and arguably Marvel Ultimate Alliance 2).
There IS also Nier, a Square Enix game. As a wise man once said, the combat is functional if a bit boring*, and the characters are slightly above average.
*I enjoy the combat, though it is rather unpolished. And the story does seem to have a small amount of self-parody in itself, so if you can read between the lines really well, you could find it very amusing.
And I guess you could also consider Fallout 3/New Vegas, or possibly The Elder Scrolls IV: Oblivion, for a more sandbox-y type of game.
EDIT: I doubt the PSN is up or anything, but there's also DeathSpank, a comedic action-RPG made in the style of a graphic novel with gameplay similar to Diablo.
And I hesitate to say it, but you could also attempt to try Two Worlds II, which is another fairly open-world game, but it does have a fairly. . . unique story, until it gets bogged down by all of the side-quests that a lot of WRPG's have.
