The thing is, though, that as a reviewer it's not your job to make guesstimates about how much "your readers" (no doubt a diverse bunch) would enjoy something, but to explain how much you enjoy something, and why.
Yes. And no.
Look, first, there's something inherently wrong with the way many reviews are structured. I'd say the standard for reviews should be stacking up facts and relative objective analysis of a game before presenting an opinion that is clearly and unambiguously derived from the facts. In fact, I'd say this standard has something self-evident about it, making it all the more odd how few times one can see it in professional reviews.
Using that standard, it matters significantly less what your audience is. You're giving them facts and you're giving them a set of logic that they can follow. They can build their own opinion on that exactly because the facts are facts and because the logic is structured in such a way that they can clearly see if this is the kind of reasoning they can agree with or not. That is why this method is superior, I would say, to just stating opinions.
But as someone who has written for pretty diverse types of sites (from an over-specialized over-opinionated fansite like NMA to a general RPG specialty site like GameBanshee to a mainstream generalist site like GamerNode), I've learned it's not all that simple. There's two factors in particular that stick out like a thumb:
1. How much do you write and what do you focus on when writing? Internet reviews are theoretically limitless, but not even the Watch and GameBanshee audiences would read a 40-page review of Dragon Age or Fallout 3. I feel more comfortable writing a 4-page review for GB than for GN. And given the text-limit reaches no more than 1000 words for GN, I have to pick and choose what to discuss and how much. So how do I choose? I have to guess what my audience is interested in. I could focus purely on what I care about but I'm not writing for myself.
2. Marks. Personally, I hate grading games but hell, it's what everyone does. Summarizing an entire field of plusses and minuses, opinions, yesses, nos, buts and howevers into a single grade as an exercise in asininity, as evinced by how long I've been agonizing over my Risen grade by now.
What makes them extra painful is that I'm well aware that easily half my readers read the intro, conclusion and grade, if that, and many only glance at the grade. Obviously, the most important thing in giving out a mark is how much I like a game. But it's also a form of recommendation. If I'm reviewing an Avernum game, it'll usually range in the 7s for GB. I couldn't possibly recommend it to GN readers, so I might have to give it something into the 5s if I'd ever review it there. Which is exactly why I don't.