At first his appearance was unimpressive; without being fat he was short and fairly solid, almost stocky, usually dressed in unremarkable grey tweed. It was when he was seated that one became aware of the nobility of his forehead, completed by the curve of his aquiline nose, on either side of which was a pair of shrewd, hawk-like eyes.
Ms. Garnet, why are you telling us that someone's appearance was "unimpressive"? That's an editorial judgment on your part. Show the reader what the person's appearance was. Let the reader decide if it's unimpressive. (And BTW, the semicolon is wrong. It separates two complete sentences. Make them individual sentences, or else separate them with a colon, not a semicolon.)
"Without being fat, he was short": What does short have to do with fat?
"Fairly solid"? What does "fairly" mean here? For that matter, what does solid imply, in terms of appearance? A bowl of day-old Jello is fairly solid (arguably). A piece of modeling clay is fairly solid. What does it mean for a person to be fairly solid? I get no mental image from this at all.
What is "almost stocky"? Is that like "almost pregnant"? It seems to me someone is either stocky or not stocky. Almost stocky is like saying someone is almost tall. It means nothing.
"Usually dressed in unremarkable grey tweed": Why "usually"? You're telling us how he usually dresses?
And again, Ms. Garnet, you're editorializing with "unremarkable." Why are you telling us something is unremarkable when you should be showing the reader what the guy is wearing and letting the reader decide if it's unremarkable? Doesn't grey tweed say it all? No one has ever looked at grey tweed and said "Oh my God how remarkable! Look at that! It's grey tweed!" So stop editorializing.
I don't know what a noble forehead looks like.
I also don't know how a forehead is "completed" by a curved nose. And by the way, aquiline means "curved down like an eagle’s beak." Hence to say "the curve of his aquiline nose" is the same as saying "the curve of his curved nose." Stupidly redundant.
"On either side of which was a pair of shrewd, hawk-like eyes." Let me get this straight. On either side of his nose he had a pair of eyes? Wouldn't that mean he had four eyes?
"It was when he was seated that one became aware [of his appearance]": How does a person's appearance depend on whether the person is seated or standing? Specifically, how does being seated bring out the "nobility" of a person's forehead? Isn't your forehead your forehead, whether you're seated or not?
The passage comes down to this: We see a short, stocky man in grey tweed, with hawk-like eyes and a curved nose. That's all. Anything else the author was trying to say failed miserably.
I give a failing grade to the writer, the copy editor, the acquisitions editor, and any agent that was involved in signing off on this horrendously foul-smelling bit of verbal excrement. One hopes the same stench doesn't extend to the whole book. I won't be reading it to find out.