This one takes a more light-hearted tone than the others, which I appreciated. The writing is good, dialogue is good, and there's a lot more humour here than any other Splinter Cell, which makes the characters much more likeable. It's still essential to take things slow and to plan things carefully, and the game does a fantastic job of making you feel like a super spy.
Your moves are expanded even further from the last two games, and there are new ways of interacting with the environment that give you tons of options. The new sound meter, which works cleverly with the noise of your surroundings, adds another layer of strategy to the gameplay. I love the way the NPCs begin to act terrified if you mess with them from the shadows, and you can really "stalk your prey" if you want to. The way you can freak them out and misdirect them is a kind of subtle power-trip that I didn't experience in any other stealth game until Dishonored came out. The way the NPCs talk to each other in general makes them more human, and the AI is better too, having them coordinate in interesting ways, which breaths new life into the gameplay.
My favourite thing about this game is the level design. The game is just perfect at giving you freedom to approach situations how you want, while at the same time keeping you on a fairly linear progression through the map. It's kind of a balance of player choice mixed with a deliberate pacing that makes the level design in this game so damn good. The Bank Heist level in particular is pretty much a work of art, but each level is very well designed and very memorable. The game gives you so many options through interactivity with the environment that I'm still discovering new things to do in these levels 13 years later, and I've played through them more times than I care to count.
It comes so close to being a masterpiece, but sadly still makes the same mistake that the previous games in the series made... It forces combat upon you in the last few levels. It is possible to avoid most direct combat encounters (not all of them), but the game starts putting you in hectic situations where shooting your way out can become your best option. I find this to be a very lazy way of escalating a stealth game, the mechanics aren't suited to it, and it's just frustrating. The only other thing I can think to criticise is the shameless product placement. Airwaves gum, Axe bodyspray, and Nokia phones are all over this game. I wouldn't mind if it was more subtle, but it's not.
Still one of the best stealth games I've ever played though. Maybe even the best.