Polygon is basically ran by a bunch of MS fanboys disguising as game "journalists" their view on anything Sony related is rather slanted on the negative side and their views of MS are quite rosy, it would be funny, only if they did not take themselves so seriously... now 7.5 for a game like TLoU is arsh at best, I think the person may not have understood what was in front of them and they should not be allowed to review anything else than COD or Battlefield titles... On the bright side, their web site looks awesome.
Gamespot is all over the place in therms of coverage and opinions/reviews, depending who reviewed it, an 8 is not just "decent" this is still a really good game, but it has a score that reflect that it may not appeal to everyone, a lot of your own favorite games may fall into this category.
Now I can see why someone would be less pleased by The Last of Us than by Titanfall or some other variation on the millitary/sci-fi shooter type of game, the pace is much slower, every enemy is a potential threat to your life, and your wing mans/squad mates don't generally kill them for you in the single player campaign.... However, it builds tension in every encounters, you need to stop and plan, manage your inventory, it challenges you in a different way than other games do, not just by putting more enemies on the screen (I assume reviewers who did not find it challenging played it only on easy because even normal is demanding for many people) it's not extremely linear, in the sense that a lot of encounters can be played in completely different ways.
Personnally however, I was more than pleased with TLoU, gameplay wise it was tense and challenging, and like A LOT of people I found it good enough to re-play in the last year AND will re-buy it, story alone would not make me re-buy it... if you think that the let's play video gave you an idea of what playing TLoU is, well you must think watching pr0n is the same as being with another human.