i know im a rare case but i like game review sites and i like ign. i haven't considered them gospel for many years.
i don't go by any one site for a review though.
typically i'll first check ign. beyond just the score, i'll actually read the review and read their reasons for giving the score.
next i go to gamerankings.com and check what game review sites/magazines are saying on the whole. sometimes it matches up with ign, sometimes it doesn't.
however, i've been playing games long enough to know the type of games i'll dig. i know i wont be into games like the new dynasty warriors or mass effect. nothing against those games or people who like them, they're just not for me. i do happen to dig some games that may not even score too highly on the whole like mr mosquito and gauntlet legends: dark legacy. the reason i take a risk and get these lower scoring games is cause i read the reviews and decide that there is enough in these games for me to want them at a budget price. even then, i still see why the games generally got lower scores (6s, 7s).
so for my general gaming updates, i like ign. you may not always agree with them but that's why there are hundreds of review sites/mags because no two opinions are alike. that said, there are certain elements that help all games reach the point of being considered great by the majority of their target audience.
are the graphics good? are they're issues like framerate drops, clipping, fog, etc?
is the sound good? is there variety is the music, fx, voice clips, etc?
how are the game mechanics? are the controls responsive, is the camera reliable (if the game uses one), does the button lay out make sense, etc?
how is the game design? is it a reasonable length, are the load times short, is there a reason to come back to it after the main quest (if there is one) is over, etc?
so, since you've pointed out that ign gave NMH an 7.8, let's go with that.
in the review, bozon noted several times that he thought a good portion of the game was great. he also noted large issues like a poorly designed open world hub and lack of ability to restart missions on the fly. still, in the review and in the podcasts, statements made about NMH were generally positive. it's an example where people just see the score and don't read the text. he even said, (more or less) "if you're a hardcore gamer, buy this game."
anyway, that's my take.