The RPG elements are basically confined to leveling up six abilities (three shared per character, three unique) that have three tiers, and three minor upgrades. You also get new equipment that comes in various qualities (rare, epic, crude, etc) but, given that the game is based more on Gears of War than anything, weapons and armor are directly swapped rather than using a "proper" inventory system. It's an action-adventure game with a cover system and very light RPG elements. However, you're deeply rewarded for exploration with better weapons, currency for ability upgrades, etc.
The plot starts off rather thin, but builds up rather nicely. The tropes are laid on heavy and they never let up. Not a bad thing, but be prepared for cliches the second a character speaks. There are lore entries, and the backstory is rather well fleshed out - it's not entirely unique, but it has its charm
Also: co-op is spotty. I'd use Hamachi and play over LAN if you have a partner (singleplayer is quite fun, don't doubt that) as the game uses Gamespy for multiplayer. If you ever played Borderlands, or anything that used Gamespy before it, you know it's a pain.
All in all, if you like any of the following (preferably more than one of them): action-adventure, hack and slash, co-op, lighthearted dark fantasy (bit of an oxymoron, I know), or dungeon crawls, the game has its merits. The menus can be a bit clunky using mouse and keyboard, but they work. If you're willing to overlook some faults, you'll get some good fun out of it. The map creator also adds a good deal of re-playability to the game.
tld;dr: Posting a review instead. For the sake of the OP, RPG elements are light, plot is pretty good, if cliche. Journal entries fill in the background as you go.[Edited by Shotgunmaniac, 6/1/2011 11:36:38 AM][Edited by Shotgunmaniac, 6/1/2011 12:42:43 PM]