There's way too much reliance on the story, the most glaring symptom of this being the fact that it makes you come back to the same boring map on four separate occasions to complete a laundry list of busywork objectives. The story itself veers in the opposite direction from the promising lighter tone that Chaos Theory had started to establish, making everything much too grim and serious, and permanently damaging Sam as a character. Conviction was criticised for its tonal shift, but people forget that Double Agent set the series in motion down that path, it's just more subtle here.
The game is noticeably simplified and dumbed-down from Chaos Theory. There's no sound meter anymore, and your visibility level is no longer a scale, but instead only three set points, which could be described as "invisible", "visible", and "noticed" (getting shot at). In most levels you don't have anywhere near as many options on how to proceed through the map as you do in Chaos Theory, which was one of the best things about it, so there's a severe devolution in the level design too. The way you navigate through your weapon selection, read information on computers and crack safes is extremely clunky. I'm sure it all works fine on a game pad, but I'm playing on PC, so it should be assumed I won't be using one. It's also buggy, with problems involving parts of the environment disappearing at certain positions or camera angles, and I had several CTDs. It's noticeably unpolished in general, and for some reason the PC version doesn't look as good visually as the X360 and PS3 versions.
The majority of the game takes place in broad daylight, tending the game more towards action than the stealthy darkness that was characteristic of the series up until this point. The accuracy and stability of shooting is much better, so the game really can just be played as an action game, and sometimes the level design encourages you to do so. When you are creeping around in darkness, the darkness itself is less defined; so not only is it very difficult to know where exactly you'll be able to hide from your enemies, but it also means that most of the time you'll be crouching in full visibility but the game will consider you fully hidden. It's confusing, looks silly, and makes everything about trial-and-error rather than strategy. It's almost impossible to go pure stealth and avoid everyone, because the game just isn't designed that way. If you want to have anything close to an enjoyable time with this game, the best you can hope for is to quietly kill or incapacitate a lot of enemies in your path, as the game never affords you enough options to realistically remain hidden all the time.
To the game's credit, the Shanghai level and the Cruise Ship level are actually quite good, for the most part. Both are interesting and memorable (although the latter is another bright level), and while they still don't play like classic Splinter Cell, it nonetheless seems like things are improving for a while... But then it all culminates in the last mission, which is the worst of them all. Painfully dull and frustrating to play through, very bright, tortuously long, and encourages combat throughout. If the rest of the game didn't put a sour taste in your mouth, the last few hours of it certainly will.