This version of the game was made by Ubisoft Montreal (who also made Chaos Theory), rather than Ubisoft Shanghai, who made the PC/X360/PS3 version. Though both games follow the same basic plot and take you to similar locations, they are otherwise completely different from each other. This one has much more in common in the first three Splinter Cell games in terms of gameplay; sneaking around in darkness and misdirecting enemies, or avoiding them when possible. Pure Sam Fisher. The story also makes more sense in this version, is a bit more grounded, and has more interesting moral choices that have direct consequences on the missions themselves. It's more of a slow-burner than the other games and takes a little while to get going, but stick with it, it's worth your time if you're a fan of the series.
It's not on par with Chaos Theory, as it doesn't have the charm, doesn't have the same level of interactivity with the environment, and the level design is too simplistic to give you as many options on how to approach situations. I thought there were too many instances of the game forcing you to kill/incapacitate enemies in order to continue, and the boss fight at the end is kind of shit. Also, if you played the rest of the series on PC, like I did, you'll find it to be a significant downgrade in terms of graphics and controls. Still, it is a very worthy Splinter Cell game, and I'd put it slightly above Pandora Tomorrow in terms of quality.
I knew this version of Double Agent was different, but I didn't realise it was better than the PC version of the game in almost every single way... The other version is a mediocre game that was a big disappointment to me, but this one is actually a great game. Sad that it was overshadowed by its shiny but shallow brother.