It feels different and great story telling might not be enough to overcome repetitive gameplay
About the story - it is told in retrospect by a friend of Sam - Vic. This makes for some chilling line like "The Sam Fisher you knew is dead. America killed him (..) and the Agency killed him..". The end sequence also doesn't disappoint. Well the story is a solid element in this game complete with signature voice but, alas, we will not hear any mission briefings by Lambert.
The setting is quite ok - museum, amusement Park, Iraq (this one feels odd), Third Echelon Headquarters and the White House. There is also some generic warehouse, a lab and a lot of streets which feel entire generic because they are well... just streets.
The characters are ok, Sam wears more casual clothes and thats a bit of a disappointment, he only gets the goggles later on. One thing that makes it less fun is lack of good camera work to see you character. And when everything turns black and white it is hard to enjoy the visuals. The goggles are different now, enabling you to see through walls but it is all in black and white and it doesn't bring the menace of a three green dots hunter on the calling like it once did. The main antagonist looks dangerously close to that colonel in Fallout 3 - is there nobody to tell him that long trench coats look stupid on a agency director? This loose dress code belongs more to Metal Gear than Third Echolon but whatever. His look felt stupid for me.
The gameplay well... it is entirely different. Sam in no longer with Third Echelon and some early previews showed him interacting with surroundings more - like blocking the door with a file cabinet or a chair. Guess what - it is all gone. You can't pick up anything at all (apart from guns). That means you can't throw a coke can or anything. You also can't knock on walls or whistle and the only means of distracting guards is your gun or gadgets.
Well, it is so because the new Sam, free from any superiors is entirely focused on killing. So, naturally, you also can't interrogate random guards for small bits of information. But about the action:
If you kill a guard in close combat you get an execution to perform. Basically you indicate which guys you want Sam to kill and he does so with the press of a button. The weird thing is that different handguns have different number of executions it can perform - how is that. Say USP can kill 3 guys quickly an Seven-eleven 4 of them - why? Anyway Sam can still climb walls, climb pipes, hide in shadows, grab guys. But it all boils down to shooting the light and running to the next cover, then peaking out to take down another guy. You can do executions and sometimes it will be your only option because you can't move a body!
One seemingly dramatic difference is that at at least two points you will be swarmed with enemies. Yeah, Sam is still vulnerable and in earlier games there would be almost no way to take them all out. In conviction it is pretty much your objective to kill them. One of this situations involve a computer room where you have to protect the computer terminal until the data uploads or something. I don't know if I was careful enough but I managed to kill like 16 guys by hanging from a pipe! Also the notion of Sam killing everyone - it is quite stupid - I killed almost everyone in every mission and it was pretty easy. The final body count must have been in hundreds. And that is nothing like the name of the game implies - Splinter Cell. Yeah you sneak a little but in the end you are one man death squad.
There are some missions outside campaign where your objective is to "sanitize the area" but you can hardly tell them apart from normal ones. The difference is that there are some interrogations made by Sam. The ones you have seen in the trailer, talk and hit the guys against the sink, mirror, grill, electric controls, a piano and so on. It is hardly any fun since you can only walk around 3 things that can obviously be used to splatter your guys blood all over. So the whole game consists of "kill everybody". Even the final scene reflects this - you have to mark 6 guys and press a button to quickly dispose of them. It seems like it is a part of the games mechanic but then Grim takes half of them out so it is just a cutscene that asks you to press some buttons first
Oh, about mark and execute mechanic - There are certain guys that cannot be killed with a shot to the head for some reason. But the same guys will be killed with the same gun when you mark and execute them. It is not consistent.
You also get the arsenal of weapons accessible at certain points of the game. Each weapon can be upgraded 3 times for in-game achievement points. Why 3 upgrades? And, more important, why would we use other hand guns than the default? I don't know, oh, it has more executions, which is ridiculous. The submachine guns are worse because you never need to use them. Also the silencers don't help machine gun fire that much so you are exposed quicker. I would appreciate it if there was any reason for using one weapon over another. Oh, they do have statistics like power and reload time (don't remember) but whats the point of firing one lethal and loud shot when you can just silently fire twice? And two shots to the head are the most any enemy can handle.
Oh, the originality. I did kill the corrupt vice president once I think (in Hitman Blood money), also inside White House. Same goes for a EMP struck Washington, DC and total chaos like in Modern Warfare 2
The music, I didn't really pay attention to it. During the cutscenes, where you can listen to it freely, then there is only a interrogation with any ambient sound or some dramatic story with a generic background music for "Sam has nothing to loose" and "America killed him" moments. Unlike Conviction, Double agent had some memorable musical themes.
Overall, the campaign is very brief, than you can play co op and some side missions but it pretty much the same experience. Without many gadgets and cool moves from the previous games Sam Fisher becomes just an assassin almost without stealth approach options. Though Whats the point of stealth when you can just as easily kill everyone. Rent it for a day and you will get most out of it.