A great game, worth playing...
To begin with, you start with the usual Splinter Cell mission, with some of the new features (mainly lethally killing things or spy moves), but soon to find out after this mission, Sam's daughter is dead. He then goes in the typical downward spiral, before Lambert (his NSA superior) offers him the chance to get his life back. Go undercover and help us save the world again!
Your job is to infiltrate the John Brown's Army (I don't know why either), a small terrorist cell that's showing up on the radar. This starts off with yougetting chucked into prison, helping out a member to escape, after thatm you enter their world, and their base. This starts off the first of four little missions in which you sneak around their base and complete objectives to keep both sides happy. Why? The Trust meter, in order to stpo one side blowing your head off, you need to make sure both sides Trust meters never hit zero, or it's game over. This can be fairly easy to do, depending on difficulty.
Most gadgets are still there, somehow your SC-20k pops up in the arsenal again, with the standard NVG's. Some new additons are added, and completing some objectives unlocks more gadgets to use.
AI in DA is intelligent, but I wouldn't put them in charge of my base, sometimes they can stare at you and think 'Did I see something? Guess not, oh well...' and stroll along.
Double Agent throws a little more light into the game, it's not all pitch black, far from it. You need to have your wits now that it can be broad daylight, although the only thing that means is a better Stealth Score (like a How Pro you are score) in which you don't need to bother with.
Co-Op is no longer a bunch missions working with the main story, it's now like a Versus Match with the AI, this can be good fun, although the lack of Splitscreen means only Gold Members can have fun. Versus mode is better than ever, and unfortunately shows how better it is then the Campaign, which although is fun, it's lacking in the Splinter Cell theme.
Double Agent is rounded up with 3 endings, depending on how evil you've been, you'll see one, one of these features a bonus mission, which is good fun. However, none seem to really appeal to make you play the Campaign again.
In all, Double Agent looks fabulous, and the Multiplayer is too boot, while some may find the Single Player lacking, the game is still worth every penny.