I usually put around 20 or so hours of game play into a game, just to understand all of its features, take a hard look at its graphical quality, understand its mechanics, adapt to the controls, get a feel of its game play...I can go on forever.
But more importantly, I play a game about 5 or so times before I write a review.
Five times is a bit extraneous. As someone who often writes reviews as more of a hobby than anything else -- just try to give an honest opinion about the game. Try to cover what is good and what is bad, and explain how the various mechanics of the game work together. If there's something particularly mindboggling good or bad, then you can focus on that, but still try to take everything into consideration. And don't worry about review scores.
Depends on the game. Quite a few games are rather short and do require multiple playthroughs to see and do everything you can see and do in the game. Most shooters are only a few hours long, so you can easily play through them twice in one day. I know some of my games here are only about 1h long.
And I guess you replied to the wrong person. While I do write reviews, I did that for a few years already, I know how I like to write them and I have no questions about it.
It might be a good thing to put in a personal touch when you write the reviews. If you get hung up on something, that might be odd to adress, maybe do it anyway. One of my favourite odd comments was in a review of ratchet and clank. "Clank laughs like Scooby Doo. It's neither funny, nor charming."
Be informational, things like estimated length of a first playthrough (try ± 2 hours of your own playthrough if you didn't get stuck for an absurd amount of time), controls, any technical problems (crashes, FOV problems, widescreen, multi-monitor support) should be included.
Example: Combat is simple/easy --> I got a Dragon's Tooth Sword and 1-hit killed every encounter from then on.
Adjectives like "fun", "good", "great" or phrases like "probably one of the best indie horror games of this decade, you will most definitely shit bricks", aren't very helpful when describing something to someone who hasn't experienced it. And what may seem to be the greatest game you've played, might play like utter trash to someone else, vice versa.
And if you're going to talk about graphics, share a screenshot (preferably without any downscaling), gets the point across faster than writing about aliasing, texture resolution, and whatever.
Wow, thanks for all the helpful tips! I've written reviews before (for plays, performances, etc.) and how I usually do them is splitting them up into different aspects of the event/entertainment that I enjoyed/didn't enjoy.
I was thinking of pulling some screenshots of the game off of google images or steam exactly for that purpose, as my computer can barely play graphic heavy games. Sometimes a picture is a thousand words.
By the way, have you played Amnesia too? The comment about shitting bricks because it was so awesome clued me in that you possibly have.
Just be sure to prioritize giving a good objective description of whatever aspect you're writing about over your opinion of it.
I don't know about actually pulling the screenshots and hosting them on your blog; you would be putting something up there you didn't make yourself. But you can still mention your computer specs and frame rate, so people get a clear idea of how well the game may run on their systems, and/or give a link to the screenshot gallery on Steam.
I have, at parts, from playing a few sections while visiting a friend. I don't actually own the game.