I am also thinking of watching it a second time. 

some thoughts after first watch 

(i) it will definitely appeal more to critics ... it appeals in terms of style, and to some extent, shock/violence ... as for the story, shld i credit the author of the book or the director/scriptwriter? ... typically, critics would be able to draw out the many subtitles/analogies, etc ... BUT for mainstream audience, i cannot be too sure ... to some extent, i am rather inclined to say that "Atonement" may resonate with mainstream audience much better "emotionally" ... it is much easier to comprehend ... 
PS: From a "literature" point of view, "No Country" may be better ... 

(ii) is Javier really in a supporting role? ... it is no secret that he kind of stole the show ... but frankly, what i want to say is ... if an audience is not aware that Javier is in a supporting role, and is asked to state who is/are in the lead roles (not based on who acted better, but who they think the director has cast as the lead in the film) ... i do suspect that many would identify Javier ... my point is ... is Javier's nomination as a "supporting" role a strategic decision by whoever submitted him as a supporting actor? 
PS: my doubt is in no way a question of his acting ability ... instead, i really thought he came across as the lead ... (cf. Mystic River ... there are 3 leads?!) 

(iii) i am rather divided ... on one hand, the minimal soundtrack makes it realistic ... on the other hand, i thought the film might have chilled and thrilled even better with a well conceived sountrack ... as of now, it might be too silent at times ... 

(iv) i am okay with the ending ... i am also okay with the "non resolution" and "non explanation" of many things ... 

FINAL POINT: 
let me watch "there will be blood" and "juno" this weekend before i decide which i prefer ... 
i have watched Atonement, Michael Clayton, No Country For Old Men.