My only issue with the Killzone reviews is Battlefield 4. A game which received many a similar criticism of "rubbish single player; but great multi-player" yet is sitting a full 14 points higher than Killzone at the time of writing. The content of the reviews I have read of both didn't seem to match the discrepancy in scores.
I actually thought the Killer Instinct reviews were incredibly fair for the package that's there. It was reviewed in a similar manner to something like, say, LittleBigPlanet. The base provided means potential for a fantastic future is there provided the users deliver the content. In a similar vein, the base provided here has potential for a fantastic future if the rest of the content delivered is as good.
Though, on the other end of the scale you've got Ridge Racer Vita. A game scoring 44 on Metacritic despite a solid base (which I can testify it does have, having played the game) with the promise of future DLC to flesh it out. So in that respect, I actually believe reviewers were incredibly leniant on KI.