It feels awkward to give a famous author a less than favorable review.
The writer of the sentence is not giving the author a less.
Less is not a noun.
The complete noun phrase is a less than favorable review. This is the direct object of give.
Less than favorable means not favorable.
Another way to write this is
The writer is giving the author a review that is less than favorable.
a less than favorable review
a review that is less than favorable
This is a nice way of saying
a bad/negative review
"A less than favourable" review is an euphemistic way to say:
- "a bad/negative" review.
This follows the general pattern in English (as in other languages) of using "not very" to imply the opposite of what a modifier usually means:
That building is not very tall (the building is not tall)
His moral character is less than pristine (his moral character is not good)
She doesn't think very highly of that movie (she has a low opinion of the movie)
The nuance varies between each of these. The "not very" construction can imply somewhat the opposite or completely opposite depending on context.
In this example, a "less than favourable" review is a bad review. The "less than" is a euphemism, a word or phrase that sounds better than it actually means.
As with many things in English, it's important to listen to how native speakers use this construction, and practice it yourself where appropriate.
Side note: Favourable is the BrE spelling. In AmE it's spelled favorable.
This expression is a great example of a common rhetorical device formally called litotes, but more commonly known as "understatement". In this case "less than favorable" is a tongue-in-cheek way of saying "unfavorable" with the understanding that anything less than favorable is in a category of being not favorable. "Less than favorable" understates the fact that it is indeed the opposite of favorable.
Another example would be "I could(n't) care less", for which there is roaring and raging debate that only saying "couldn't" communicates the correct meaning of "I do not care".
A less controversial example would be "He was not a little surprised by her return", meaning "He was very surprised by her return".
A "less than favorable review" could mean a bad review.
In the case of a famous author, it is likely to mean a "lukewarm" review. Something like "okay, but not great."
That is not a bad review, but not as good as one would expect, given that the author is famous.
This is known as "damning with faint praise."