Chaos Theory was an amazing game, I think it's pretty universally accepted that it's the perfect Splinter Cell. Still don't have Conviction though, really need to get around to buying that.
Here's my official review:
It's ALMOST a completely different game. There is no hiding bodies, and you can either use people as human shields when you sneak up on them or you can immediately kill them, much like in Chaos Theory. However, the mechanics are different and Chaos Theory just felt so much more, well, FLUID.
However, the mechanics of shooting around corners is the greatest thing EVER. It's much, MUCH smoother in this game. It seems like this one was made to be much more fluid in getting through the levels; sneak up, smack around/take hostage/break neck/double tap after kicking his knees out from under him/twist hand and kill him with his own gun/etc. Levels were more seamless and the story was done a bit better but still, the gameplay itself had me longing for the mechanics of Chaos Theory.
I remember when they first started doing this project and they showed a demo of Sam throwing people around the room and shit...this was maybe 2 years ago. I remember that demo and was really blown away, but none of that is in this game. I guess they scrapped it for the more conventional SC mechanics, which is good and bad.
One of the coolest things now is the new Deniable Ops mini-games they have. You choose one of two new characters and do the whole sneaking/killing through levels that are really about the same size as an entire SC stage. You can either be a hunter or last man standing and to tell you the truth, I had just as much fun playing those things as I did the game itself. Each scene is made up of 4 parts and you must progress through each part to reach the end. If you're spotted or do some stupid shit, more people will come after you...like A LOT more. It's really challenging.
Also I liked the "traps" they've set in this game. You can shoot down dangling objects like chandeliers or heavy art pieces hanging from the ceiling and crush people underneath them. There are a few new gadgets that are pretty cool, and I like the ability to grab any gun in the game that's dropped. You can upgrade weapons and such and have weapons caches placed throughout each stage if you'd like to change weapons.
It's a great game, but after you play it, you'll know what I mean when you start thinking about Chaos Theory. I mean, remember the security company you had to break into, or the ship you had to scour through, or bank you had to break into in Chaos Theory? Those are still head and shoulders above most of the stuff in Conviction. However, Conviction is different in the way that there isn't any loading screen, saving, etc. It's one continuous action so it feels much more story-driven than Chaos Theory.
You'll dig it a lot, but I'd download it first like I did in case it isn't what you were expecting.