I think that the writing style described by Milen above may only hold for American games mags. In the UK, games mags tend to fall into two camps : those written for kids (a la Computer and Video Games), and those written for adults (or at least, twentysomething kids), such as PC Zone. The kids mags tend to read like Viz, with good games getting glowing reviews and 96+% scores*. There are generally lots of in-jokes that only sad people of similar age to the writers will pick up on (such as Mind The Oranges Marlon). The "adult" mags adopt a stricter reviewing policy, and can only describe any game in terms of others in the same genre that have gone before it, leaving newcomers to that genre totally mystified. The toilet humour is ramped up to the max in either case though.

I think the difference in writing style stems from the fact that the US never had a mag like Your Sinclair to subvert the tried-and-tested formula. Instead most US mags seem to be modeled after Nintendo Power and EGM, which could probably only stoop any lower if they'd removed any trace of editorial altogether. There's also the element of self-effacing humour. UK games mags tend to be quite jokey. Attempts to sound "cool" would not endear a reviewer to the readers and would look very out of place.

In any case, the games journalist knows that the only part of the review that's going to be read is the score, regardless of writing style.

* Although at least in CVG they quietly make an apology a few months later if they go a bit too far.