I only played about half of Silent Hill 2 (I rented it, enjoyed it, but ultimately never finished it), so I know just enough about the series to enjoy some of the stuff they pulled from the games.
POSSIBLE SPOILERS, MAYBE?
I absolutely LOVED the first half or so of the movie. Absolutely and completely. Everything looked and sounded incredible (Well, except the acting). Pyramidhead was visually perfect, despite being completely irrelevant to anything else that was going on in the movie.
I felt absolutely no attachment to any sort of story arc being built, but I greatly appreciated how incredible everything was designed, and looked. I think that's why I stopped enjoying the movie once it became intensely involved with the actual plot. It stopped being as fun to watch, for me. I understand that it's crucial for movies to have plots, but honestly, the atmosphere that was so aptly forged by the first half of the movie kind of crumbled away (but not without a few exceptions). The whole plot involving the cult seemed to lack any subtlety, and I just couldn't find myself staying interested in it. I wish it could've just kept on doing what it did earlier, maybe just hinting at what was really going on, instead of shoving it down my throat. Or if the movie stopped there, I would've been pretty happy too, because it felt like it dragged on for a really long time.
Again, I have only played a portion of one of the games, just enough to get a superficial understanding of the games' style, and literally no understanding of its overall plot, so I'm sure there are probably tons of you with a better appreciation for the series who were able to enjoy what this movie's plot had to offer.
But, even with its faults, this is by far the finest video game-to-movie adaptation I've ever seen. It's great to see that some games can have their atmosphere left intact while being transferred to the big screen.