Below is the rather exhaustive Silent Hill review I wrote in an e-mail to a friend of mine back when the movie first opened. I will warn you though, that its rather long and filled w/ spoilers. I figured I'd post it here in "honor" of the DVD's release in a few days. 
"To begin, I had a mostly favorable opinion of the movie…It wasn’t the greatest piece of cinema I’ve ever encountered, but it wasn’t the worst either.
Concerning the accuracy of the movie (in comparison to the plot/events of the first game) I would place it within the 40% - 60% range. However, these are my own arbitrary numbers, as who is to say how much certain elements count as a percentage, and so on and so forth.
What I liked most about the movie were the parts where the game was accurately recreated (or close to it). The part where the mother first loses her daughter and she is running through the alleys and the alarm sounds to signal the coming darkness...it honestly gave me chills. That is basically taken straight out of the first 5 minutes of the game. Even the disorienting angle of the camera during this scene and the loose manner in which it pans and zooms is an exact replica of this scene. Very well done!
They also left the locales in tact, i.e. the school (Midwich Elementary School), the hospital (Alchemilia Hospital), the streets and their names etc. In an interview prior to the release of the movie, the Director (Christophe Gans) admitted that he was a huge fan of the first game and that he wanted to do it justice on the big screen. In my opinion, the film was a labor of love that lost its way somewhere along the line (I will discuss how in a moment).
Another thing I also enjoyed about the movie was the homage paid to the enemies/monsters. The monsters of the game are meant to be the most terrifying combinations of mangled flesh/bone/foreign material the human mind could imagine. As such, there are light S&M elements that are present in the some of the monsters' appearances. They did not censor that for the movie, rather, they embraced it. Good show.
Now, on to the things I did not like, first and foremost were the selective edits made to the original story. Probably the most puzzling of these were the characters chosen (or in some cases, not chosen) to appear, or were made to appear as tokens. The mother does not go with her daughter to Silent Hill in the game, her father does. In the game, the mother has died before the events of Silent Hill take place. The director was quoted saying that he replaced the father (Harry) with the mother as the father was acting from maternal motives/feelings in trying to save his daughter. The writers and director felt that the desire to protect one’s offspring from harm was better suited to a mother. This is bull****.
One of the novelties of the first game is the fact that it is a father, emotionally and physically weak as he is, trying to rescue his daughter from a living nightmare. It troubles me that the creative minds in charge felt uncomfortable portraying a 'maternal man' on the screen. One of the core elements of the Silent Hill mythos is that the character/protagonist is weak. In his/her weakness, he/she committed some sort of regrettable act/omission and that individual is subsequently drawn to Silent Hill in order to repent. That idea, probably the most important facet of the Silent Hill series, is totally missing from the movie, and it takes away from the experience.
Then there are the useless, inexplicable additions/amendments to the story. This whole nonsense about coal fires burning and this Christobella character and her zealous cult was amusing at best, shameful at worst. Not to spoil too much of the game, but it is the mysterious cult that is attempting to summon the evil in Silent Hill, not stop it. Pathetic. The writers must have felt intimidated by the plot and sub-plots of the game that they swapped in some badly concocted story about the occult trying to keep away "the demon." While I understand that it would be difficult to cram the events of a game that is normally several hours in length into a two hour movie, I think an attempt must be made to preserve key elements of the plot. I believe this particular tweak was unnecessary and hurt the movie.
In addition, they wasted precious time on senseless detours throughout the movie including the scene where the mother finally meets the 'evil twin' replica of her daughter. The nurse (her name is Lisa, btw) at the bottom of the 'evil hospital' is a key figure in the game, for game play and plot reasons. They wasted her role by turning her into a 'place-holder character.' There is also a subplot of occult drug abuse and smuggling in the game, which is inexplicably absent from the movie (though, in the spirit of shortening the movie, I am more forgiving of this being absent than the other portions of plot that were outright changed).
Lastly, the ending is garbage. I have trouble recalling it without becoming angry. They could have at least tried to salvage some of the worse plot points of the movie by introducing the 'real evil,' i.e. the demon (Samael) that was responsible for the reality warping that occurs in the town. Instead, they attempt to appease the teens who they counted on to buy a ticket, with a splatter-fest of blood, gore and maiming. Don't get me wrong, I enjoy fictional violence as much as anyone else, but when it’s used to cover up plot holes and a lack of creative imagination, I find it offensive to my intelligence. Don't even get me started on the scene in the house at the very end. So disappointing, but for less than obvious reasons.
Phew...I'm out of breath and my hands are tired LOL. Hope you enjoyed my 'review' of sorts."
The above observations and comments just happen to be my own, so feel free to disagree (just don’t start flames, I will not tolerate that).