You play as Daniel Garner, a seemingly regular guy who has just been killed in an horrific car accident. Trapped in a dark and unwelcoming world between heaven and hell, you struggle to uncover the reasons why you've been denied entry into heaven. Awaiting your purification, you must fight through an endless number of demon soldiers as you attempt to stop an imminent unholy war. The game features 24 single-player levels, each unique with virtually no texture reuse between levels. The game also features five multiplayer modes, played out over 7 maps.
This is exactly what games should be about. Fun.
It takes the old school formula and puts it on overdrive. Many different enemy types, many different environments, tons of weapons that are basically two weapons in one (genius idea because you get to do a variety of mayhem without having to switch weapons as often), optional challenges to complete on each level to unlock tarot cards that give you a special powers.
Giant bosses that I've never seen before (unless you've played Shadow of the Colossus or Black & White)
A long list of statistics you get for a completed mission which you can compare to other players.
It doesn't get much better than this :)