It just didn't provide the lasting experience I've had with other Splinter Cell games.
I would give this a 9.5 if it weren't for one factor: it gets boring as hell. You'll have a great time with both the single and co-op campaigns, and the extra modes are pretty good as well. But, you'll get bored, fast. And that's caused by how retarded-easy it is. I breezed through Realistic difficulty on my first play through. This would be one of my favorite games if there were like, three or four more difficulty levels.
Overall: You'll have great fun with this game, but please don't spend 60$ on it. Wait till it's 40$, and it's a must-buy.