The Spiderwick Chronicles is based on the recent film adaptation of the book series. The game's title refers to a field guide that serves as the plot's central item. Years ago Arthur Spiderwick discovered an unseen (literally) world and decided to keep a journal of his discoveries. Years later, a group of kids discover the book after moving into Spiderwick's mansion, unleashing all kinds of problems. Actually, the game seems to assume you've either seen the movie or read the books since many of the plot's inner workings are glossed over. For example, the book's importance is never fully explained, nor is the reason the main villain wants the thing. While it is easy to dismiss this since "only fans will play it", some explanation might be nice for newcomers. There are also a number of small inconsistencies between the in-game story and what is presented during movie clips, though this isn't that big a deal except for people who tend to notice that kind stuff.
Gameplay is set in a semi-open world and revolves mostly around item collection and combat. Over the course of the game, you'll control all three of the kids. Although each has their own combat abilities, they pretty much play the same way. Of the three, the only oddball is Simon, whose ooze-launching shotgun makes combat incredibly difficult. The range and spread is nice, but he's still a generally weak character. Item collecting and exploration are also a major element; most chapters will require you to search for items or discover new paths through the game's interconnected world. One of the game's stronger aspects is that it always keeps you engaged. Though there are a few slow moments, there's never a point where you have nothing to do. At the same time, gameplay does tend to settle and leaves many of the more interesting aspects hanging.
As you travel around the world, you'll discover sprites, which you can catch. You can carry up to three sprites at a time and when activated, they grant special abilities or heal your character. This is a cool concept, though most of the special abilities are worthless. The only time the system is really exploited is during a puzzle that requires you to first decipher a riddle then use three specific sprites to solve a puzzle. More sprite integration like this would have gone a long way. Another underused aspect is the idea that some things are only visible while looking through a stone circle. Unless you complete a side-quest that unlocks permanent vision, you can only see sprites and goblins in a limited radius. This adds some excitement to battles since you always have to stay alert, but it could have been used for more than combat - such as discovering secret areas.
Depending on skill level, the main game takes about 10 - 12 hours to complete. Completionists can go back and try to finish the field guide, though I ran into a issue where one sprite refused to spawn in an area, which kept me from completing the guide. You'll also unlock a series of multiplayer games, though these feel like they were tacked on and aren't that interesting.