It is hard to believe that XIII is running on the Unreal Engine, but the style is pulled of well and the graphics engine does the job needed. Characters and interactive objects are truly cell shaded, with thick black ink lines and continuous tone shading. The environments are actually "faked" but it is hard to tell, unless you really look. The texture work is just done in such a way to blend well with the characters. Because of this, the environments lack the rich detail and flair seen in the well-modeled people and objects. This is a trade off for performance, as cell shading is not the easiest thing for a computer to render.
Adding to the impact of the story are David Duchovny, Adam West, and Eve. All three deliver solid performances that don't come across as over the top. The game would have done fine without the talent, but I could not imagine Agent XIII, voiced by Duchovny and played by you, sounding like anyone else.
The story starts you out washed ashore and suffering from amnesia. You are rescued by a lifeguard but quickly thrown into a black-and-white flashback that you also play through — a story mechanic used throughout the game. Soon enough you faint on the beach, and wake up in a lifeguard building. No sooner does the lifeguard call for help than she gets riddled with bullets. Better pick up those handy throwing knives from the counter and get to work.
Just as you would expect, action and drama are rendered in multiple windows on screen. A headshot is even more satisfying when you see it three times in small windows, accompanied with a the visual "Ahhhh" from the now dead bad guy.
Along with your standard array of guns such as .44, sniper rifle, and submachine gun, you have fun alternatives such as the crossbow, and even non-lethal objects such as wooden chairs and bottles. On many stages you are required to neutralize, but not kill, so these environmental weapons come in handy. Stealth also plays a large role in XIII, but you still get your guns-blazing fun too.