Pyramid Head is stated to be Alessa/Heather's guardian and executioner, in a sense taking Valtiel's role from SH3, largely justifying complaints of his unexplained presence in the first movie.
Roughly the first thirty minutes or so pretty much try to excuse all the changes from the first movie and find ways to make them fit into the games' universe, like Chris changing his and Sharon's names to Harry and Heather respectively, explaining (Or trying to, at least) how Sharon returned to the normal world, and reestablishing Harry's role in the story (and then ruining it again by killing Douglas in his place), and tying up the Plot Hole of Rose being stuck in Silent Hill after the first movie's Gainax Ending.
Contested Sequel: There's no denying that this film is much more in line with the continuity of the games, and does an admirable job of tying everything together in a way that doesn't feel too contrived. That said, there's also no denying that the script, cast, cinematography and effects are all markedly worse than in the first film. While we've all seen in action just how terrible the results of a survival horror film series straying too far from the games can be (the commercially successful but critically-reviled Resident Evil movies), there's also the question of whether or not the first film, which did have some legitimately scary and emotional moments, should have been almost completely written off in a way that creates some noticeable Plot Holes because it didn't follow the events of any of the games.
Esoteric Happy Ending: Yes, Heather saved her father, apparently defeated the order for good, and got to leave with Vincent...but out in the real world, she's still considered a murder suspect, so it's unlikely she'll get a warm welcome when she comes back home.
Ham and Cheese: It doesn't seem like Malcom McDowell was taking his role very seriously.
It's Not Supposed to Win Oscars: The common defense for the movie whenever anyone tries to point out it's countless flaws and systematic destroying of the source material.
Narm: The dialogue writing andacting in this movie are just about as bad as they were in the first game, which came out over a decade ago, and were dramatically improved by the PS2 era to create an effective mood of unease. Here it's just bad acting.
The Missionary, in the game, is a creepy blob-headed monster somewhat akin to Pyramid Head. In the movie, it's essentially a Cenobite for no apparent reason.
Special mention should go to Rose's cameo, where she only refers to Harry as "my love".
The "poptart jumpscare". To elaborate, it's a strange moment of editing where after Heather's opening Nightmare Sequence there's a sudden cut to a close-up of a poptart inside a toaster. Needless to say, Phelous has made this into a Running Gag in his reviews.
Romantic Plot Tumor: Heather has known Vincent for, what, 12 hours? And yet Harry trusts this kid he's never met before with his daughter, because apparently they're an item now.
Sequelitis: The first film was generally regarded as a semi-successful adaptation in certain circles of the Silent Hill fandom, silly plot direction aside. This one was universally panned by critics and there's a So Bad, It's Good entry for a reason.
So Bad, It's Good: To some viewers. It is to Silent Hill what Michael Bay was to Transformers.
Special Effects Failure: The makeup effects are quite good, as in the first movie, but whenever a CG monster shows up, it looks pretty awful.
Let's not forget when Leonard is killed, the shot actually slips out of focus.
They Changed It, Now It Sucks: Complaints over Vincent's age and relation to the plot have been a major complaint from fans, not to mention killing off Douglas in Harry's place, mitigating the formers role in the story and neutering a large part of Heather's appeal as a character.
They Wasted a Perfectly Good Plot: With this canon's version of Alessa being something of the Bigger Bad, the idea of Heather facing a confrontation with her was an attractive plot idea. The Alessa part of the plot is kicked to the sidelines and is resolved in a scene lasting barely more than a minute.
Video-Game Movies Suck: While some people may enjoyit, most agree that it's slow, unrealistic (the characters and the acting), and has a lot of cheap scares.