Great for kids, anyone over 12 may be bored.
It isn't that the levels aren't designed well or the game isn't interesting, it is just that the presentation is quite cartoonish and the gameplay itself if very retro - think Doom II or Duke Nukem 3D style gun and run and you're getting warm.
I found quite to my surprise that while I became bored with this game long before I finished it that my friend's children couldn't put it down. So in addition to donating the Geforce 5600 to a new gaming PC for the tots I handed over Serious Sam II and a few other titles I couldn't bring myself to enjoy like Prince of Persia - trust me, kids will enjoy almost anything so I was Uncle of the Year.
In short, a moderately entertaining retro shooter with colorful graphics perfectly suited for your pre-teen, but grown ups may decide to pass.