I've played my fair share of FPS over the years on the PC and consoles and this game, IMO, got unfairly trashed by review sites/magazines when it's really quite good.
It does have its flaws (a major one being no mid-level saves when the levels can last 30-45 minutes in length) but I found it to be really enjoyable.
The graphics are serviceable, the AI uses cover but isn't brilliant and the sound is just phenomenol. It's kinda of like playing a movie...very high tension and a real "cinematic" feel to the production quality.
It's a typical run-and-gun shooter on rails, but I'd personally give it between a 75-80 percent rating.
Well worth $20 for sure.
If still not sure, play the OXM demo from two months ago to get a taste of it from the demo (which convinced me to buy it).