It's been probably 10 years or so since I was writing reviews, and I have to say, I never felt pressure to skew a review one way or another.
The biggest heat I got was from fanboys when I had a sneak peek at PAX of Duke Nukem Forever and had to report how shitty it was. "YOU DON'T KNOW!!! YOU DIDN'T PLAY THE WHOLE GAME!!! YOU HACK!!!"
And I was like "Yeah, you're right, I didn't play the whole game, I played what their marketing team WANTED me to play and it sucked, you think the parts they DIDN'T want me to play are going to be better?"
Surprise... the game stunk up the joint.
But when it came to reviewing games, I approached every review as if the game were a 10/10, and then as I played I looked for reasons to subtract or add points. The plusses and minuses would balance out and I'd have a final score.
As a former teacher, I used school grades, which is why I think most sites are on a 7-10 scale.
A - 90%+
B - 80%+
C - 70%+
D - 60%+
F - 59% and down.
A game can be bad because it's a bad game or it can be bad because it's functionally broken. D is generally the Ralph Wiggum of games, possible to like, but you have to admit it's pretty bad.
I had to give a failing review to Assassin's Creed Liberty on the Playstation Vita even though I really liked how it looked and it played, because it had a game breaking bug that made your save file unloadable. Ubi took 2 months to fix it, rendering it unplayable for the first two months after launch.
Once it was fixed, I amended the review, but it was plainly unacceptable to release it in a broken state like that.