I think it's important in that it's the first game I've played that's legitimately comparable with a movie in terms of presentation. It's better to just watch it being played than a lot of bad movies and TV out there. The script is good, the performances are excellent and the presentation is hollywood quality. Obviously, the CG is not on the level of a Pixar movie in terms of the technology, it's being played live not prerendered, but all the artwork is of the same quality.
This is something that's been worked on for a while, and claimed many times before. In a year or two, it will be topped, and it won't be considered important in retrospect. Right now it's important because it's the best at what it does.
This thing might not be considered important by a lot of gamers. To me it's important because I don't really segment entertainment. I like movies, book, games, music, etc. So throw any of that at me in any package and I'm going to enjoy it if it's done well. It's kind of like how Rock Band is good or bad based on how good the music selection is, only Rock Band uses already popular songs so it's already successful in that respect before they even begin.
A lot of people first claimed that games were movie quality in terms of story when FF7 came along. I'd argue that I disagree with that. FF7 was great for its time but it's got a LOT of shit in the story from the script, to plot points, to stupid characters. If FF7 was converted into 20 hour television show, with the gameplay replaced with cutscenes, nobody would watch it.
If Uncharted 2 was converted in a similar way, and it was pre rendered for higher quality, it would be something I'd want to watch, in fact more than those National Treasure movies or the new Indiana Jones. Even if it wasn't prerendered and of the quality it is now, it's good enough to show and be considered decent.
It doesn't mean the gameplay is anything out of the ordinary. It's really good but it's not "important." I'd compare it to like a Halo 3 in terms of gameplay. Absolutely excellent but nothing groundbreaking at all, not even over Halo 2/Uncharted 1.
In terms of the presentation I feel like I'm playing a new level of games. When I beat it I felt similar to when I beat Zelda for N64, some tangible new level that is just a little ahead of its time to be coming again any time soon.
I'm sure every game designer has studied Uncharted 2 in depth and is working on trying to infuse some of that magic into their own storytelling, but I don't think it will be common place until next generation when hopefully the technology is such that the effort can be put into story telling as the graphics and physics will be easier.
You can also say that in terms of presenting writing into video games, Lost Odyssey was important in that in infused its story with these written segments which were really very good. Not good for video games, good for writing which is really my point, to run with the big dogs. The only thing is that while Uncharted 2 is going in a direction that will eventually be all games, Lost Odyssey was something of a one time thing. So it is important in that it will remain unique, but Uncharted 2 advances the medium by raising the standard to the same level for story as any movie or television show.
Of course, it's not an amazing story by movie standards. It's not comparable to watching the Matrix or Pulp Fiction. It's not something I will go to a non-gamer and say "you must watch me play this!" It opened the door though, and it's up to future games to rise to that level.