I don't really think that you can easily compare metacritic scores over such a long timeframe because lots of publications have changed the way in which they review games since KZ2 came out, which produces a far less granular and varied result than of days gone by.
Also, go have a look at the Killzone 2 reviews, the first review that appears on that list is from Official Playstation Magazine, who scored it 100.
And again, in a 4 year period the genre has moved on, what have the subsequent Killzone games brought to the table that are original that might score them brownie points?
I personally feel that the graphics have become less impressive relative to their release window. KZ and KZ2 in-particular were both benchmark titles.
There are lots of interesting conversations that can be had around how reviews are measured and how subjectivity can be measured with a number.
Videogames inparticular are interesting as a media because they are technology driven pieces and that is a constantly shifting bar.
(I don't fully understand the point regarding the OPM 100 score. Those mags were perfectly legitimate. They scored games fairly. OPM doesn't mean Sony publishes it or anything like that; it just means it focuses only on PlayStation games. Plenty of brutal scores given out by pubs like that.)
Anyway, without getting into the weeds of review scoring trends - which is somewhat off-topic - I think for the purposes of this topic here, it suffices to say that Shadow Fall showed a rather brutal fall-off in quality, according to pretty much anyone you might care to ask. I gave some numbers as evidence, but even without that, if you paid attention, you pretty much felt the same thing.
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I actually don't think war FPS campaigns have particularly moved on or improved since 2009, to tell you the truth. The only reason I made this thread is that other than the trappings of the PS3 -- the deferred rendering causing the input delay (I think I recall some connection), the annoying controller -- KZ2 stands up very very well against the best campaigns today. It has atmosphere and visual flair to spare, and it has a level of intensity that feels like a labor of love rather than the cookie-cutter explosion-fests that one got used to after seminal games like Halo 1-3 and CoD 4 came out and set the formula. Plus there is the unique feel of weight and those violence animations IMHO still pack a punch that most games since haven't.
But I don't know. It could be nostalgia.
Brush all this philosophizing away, and I'd simply love to play this campaign in coop.