Here are some parts within the passage where I found subtle hints of the author's attitude:
5-10 = having both qualities seems to be quite intriguing
27-30 = author sort of defends Lichtenstein's work
31-38 = author seems to be intrigued by the idea that it not only possesses the reflective power of parodies but an impulse towards realism
43-51 = "an inner sweetness"
Basically, there is no negative connotation in the passage, and just the fact that the author is going into this much detail about Lichtenstein's work without criticizing any of them, it seems like the author appreciates his approach to pop art.
(A) - "enthusiasm" seemed too strong. We definitely have no evidence to support this.
(B) - I liked the first part about "respect" but it seems like the author is more interested in how the work portrays "realism" more so than "parody of youth and innocence"
(C) - author does not feel pleasure in its blatant rejection of abstract expressionism (how negative!)
(D) - I liked the word "admiration" but the author does not admire Lichtenstein's work for subtly critiquing contemporary culture
(E) - Yay! We have "appreciation" which is not too strong but not too neutral, and we have evidence to support the idea that the author appreciates the work incorporating both realism and naivete (the last paragraph clearly supports "realism" and "naivete")
Hope this helps!