Is a book featuring a non-self aware Mary Sue automatically considered to be poor quality?

Question

Is a book where the main character fulfills all of the criteria for being a Mary Sue, and where the trope is played straight rather than for illustrative or satirical purposes (for example, the character is an avatar for the author, fulfilling a personal fantasy of theirs), automatically considered to be of a poor quality, or can it be redeemed by other qualities such as the richness of the world that it builds, or social issues that it probes?

Answer 1

The question is based on several misconceptions:

1. The idea that we can say that a book is “considered poor quality” without reference to who is doing the considering. You must have noticed that different people have different taste in literature. One person likes ornate and difficult prose, another likes a clear and straightforward narrative; some like realism, others prefer fantasy; some like an opinionated narrator, others prefer to make their own judgments. So how likely is it that everyone will “consider” Mary Sue in the same way?

2. The idea that lots of people have opinions on Mary Sues. A “Mary Sue” is a kind of author-insert character in fan fiction. But fan fiction is very much a niche genre, and most people probably have never read a book with a Mary Sue, and so almost certainly have no opinion on the matter.

3. The idea that the quality of a book can be determined “automatically”, by some superficial aspect of it (here, the presence of a particular kind of character). The quality of books is not subject to automatic evaluation in this way: any “rule” can be broken by a good writer. The reason for this is that rules are distilled from good books, not the other way round. “Rules” about writing are really observations about common aspects of good books, but this does not mean that any book that follows the rules will necessarily be good!

My point (3) was put into verse by Alexander Pope:

Those Rules of old discover’d, not devis’d,
Are Nature still, but Nature Methodiz’d;
Nature, like Monarchy, is but restrain’d
By the same Laws which first herself ordain’d.
⁠First learned Greece just Precepts did indite,
When to repress, and when indulge our Flight:
High on Parnassus’ Top her Sons she show’d,
And pointed out those arduous Paths they trod,
Held from afar, aloft, th’ Immortal Prize,
And urg’d the rest by equal Steps to rise;
From great Examples useful Rules were giv’n,
She drew from them what they deriv’d from Heav’n,
The gen’rous Critick fann’d the Poet’s Fire,
And taught the World, with Reason to Admire.

_{Alexander Pope (1711). An Essay on Criticism. Wikisource.}

Pope lampooned critics that tried to apply rules automatically, without judgment:

Then Criticism the Muses Handmaid prov’d,
To dress her Charms, and make her more belov’d;
But following Wits from that Intention stray’d;
Who cou’d not win the Mistress, woo’d the Maid,
Set up themselves, and drove a sep’rate Trade:
Against the Poets their own Arms they turn’d,
Sure to hate most the Men from whom they learn’d.

The “Mistress” in Pope’s metaphor is the Muse, the inspiration of great literature, and her “Maid” represents the rules that critics deduced from this body of work, but which cannot themselves inspire greatness.

Applying Pope’s approach to the original question:

When Star Trek fanzine writers pub their ish
They sometimes do so to fulfil their wish
To be admir’d by Kirk and Chekov too
Within the ideal guise of Mary Sue.
But those who say that narratives which would
Indulge in wish-fulfilment are no good,
Miss that those words, to boldly go, distill’d,
Are only science fiction’s wish fulfill’d.

Answer 2

The aspects that determine a novel's or story's perceived quality are not limited to the characteristics of its main character.

A novel may be considered good because of its intriguing plot or because it has a riveting story. In some cases, this aspect may overcome weaknesses in the depiction of characters. For example, I don't find Liu Cixin's Remembrance of Earth's Past trilogy (a.k.a. The Three-Body Problem trilogy) very convincing with regard to characterisation (with the exception of Luo Ji), but the story kept me reading late into the night.

A novel may be considered good because of its language or style. I was very impressed by Flaubert's prose style in Madame Bovary (coming to it after reading Prévost's Manon Lescaut). Flaubert was more than just a great stylist, but great prose style does not imply that a novel's characters will be convincing.

A novel tends to have multiple characters. If the main character is unconvincing, some of the characters may be, though possible not sufficiently to overcome the issue with the main character.

A novel may be good because it subverts the readers' narrative expectations.

A novel may be good because it makes readers look at the world in a totally new way.

Most novels are not strong in all these regards; many have weaknesses and a number of redeeming qualities. From that point of view, the presence of a non-self aware Mary Sue character needn't be fatal. However, an author who creates such a character may also have weaknesses in other areas of his writing. So it probably not the mere presence of a Mary Sue that makes a novel bad (A causes B) but both the Mary Sue character and any other weaknesses may be caused other issues; it other words, it's more like an issue correlation rather than causation.