As for the New Yorker's review:
For the most part Lane keeps the movie at arm's length, refusing to engage with it, merely trying to describe the characters humorously, but failing.
The final part of the review is the second blow, attacking the premises upon which Watchmen is built - which is no hard work, given the current political atmosphere, and the original work's admitted shortcomings - but really, all's well: There could not be two more opposite demographics than the New Yorker's, and that of comic book readers.
Personally, I have to say that I find the review biased regarding comic books: Persepolis and Maus, being realistic, grounded in historical facts, get an automatic free pass, while Watchmen, which is not ashamed of working with fantastic elements, is treated like more of the same, run of the mill super-hero stuff, which it clearly isn't.
On to the film itself:
Even though the film keeps the story's plot, structure and resolution, the most noticeable change is in tone in certain scenes, and some fans from the original work might have a problem with that. I did, but obviously I didn't think it to be the wreck I was anticipating (or I wouldn't have paid to see it twice as I did). However, the movie sells short some of the comics cleverest moments. Also, a couple of times it gets hard to shake the feeling that you're watching a big budget high school play (the final face-off between Nite Owl and Ozymandias, which, alas, was inexistent in the comic, hurts).
Expect pacing problems. Scenes don't breathe long enough for some of the big impact moments (there are many) to resonate properly, which, in a story such as this, it's a crime (this might be fixed in the restored Director's Cut to be released on DVD).
My favorite scene was a small Walter Kovacs having his hair tousled friendly by one of his mom's customers while others waited in line (It's in the beginning of the movie, in the montage sequence, only a couple of seconds but I found it really cute, made me grin from ear to ear).
My favorite character was Doctor Manhattan. Everytime he was on screen it was win time; I think Billy Crudup did something really special there. Least favorite was Ozymandias, because he wasn't the same character as in the comics, for the worse, I think.
And that's it, I guess. If you're a fan of the comic, you have reasons to care; if you're not a fan of the comic, why bother? But, if you're a fan of cinema, then this movie offers plenty for you to chew on, both because of its successes and because of its failures. I could go on and on for pages analyzing it, but thankfully being at work prevents me from doing so.