The word handsome is usually used to describe a man, however, the most naturally stylish women in the world are Italian women; they're considered 'handsome' as they don't employ cutesy tricks, frilly clothes or superfluous details - they're always chic as they're always well-tailored and simply dressed.

A Handsome Room means the same thing; well-edited spaces with good architectural bones and simple furniture. 
It's not about 'decorative' or 'trendy' furnishings and piles of schmaltzy/girly accessories.

Mr. Blass' Sutton Place apartment was so drop-dead gorgeous when it first hit the pages of House and Garden back in the late 80's that I think every interior designer re-tooled their 'schtick.'

First published during a maelstrom of colorful, chintz-laden, 'more-is-more' interiors, and yet his hyper-edited rooms were quite simply white painted walls with brown furniture and masculine objet d'art.

Mr. Blass' New Preston, Connecticut home employed the same aesthetic: Beautiful objects, slightly lower-tone brown furniture casually arranged in a simplistic, no-frills space.

His Connecticut bedroom had simple, brown painted walls, slipcovers, bare floors and very few decorations. It's total decorator porn!

(Source: David Kleinberg)
Architecturally succinct with no frills = handsome!
Mocha upholstery actually sets off the well-detailed paneling; white upholstery would've create a sea of white and details would be lost.

(Source: Marshall Watson)
English architecture and furnishings help parlay any room into a handsome one. Notice the lack of porcelains, gilded frames and patterned fabrics.

(Source: House Beautiful)
When you lose the curly-cues, zhuzhy backsplash tiles, swirly stone tops and cutesy accessories you'll have a handsome kitchen.

(Source: Giancarlo Giametti)
This room is neither masculine or feminine it's just balls-to-the-wall chic!
Each piece is perfect - the art, the furniture - and the lack of crap or superfluous lamps on each table.

(Source: Baretta Diamond)
Walk into this foyer and you'll immediately 'get it!'
White painted walls, equestrian art, plaid fabric and no carpets or schmaltzy chandeliers.

(Source: Michael Smith)
Prissy bathrooms get skanky so quickly, right?!?
The simple fusion of the honey-colored paneling, antique wood pieces with beige tones creates a very sophisticated bathroom.
The Moorish mosaic definitely adds a masculine note.

(Source: Palmer Weiss)
A typical pre-war apartment gets brought into the 21st century by simplifying, using a warm palette and classically-styled furniture.

(Source: Amelia Handegan)
What makes this traditional room 'handsome' are the books, English furniture and a very simple palette with few patterns.

(Source: Bunny Williams)
Pierce Brosnan kinda handsome!
No tsochke's, no frills, elegant antiques and brown-tones!
BOOM, there it is!

(Source: Unknown)
French and Italian antiques are combined with modern pieces to create a totally up-to-date 'handsome' space.

(Source: Bruce Budd)
Nuances of Mr. Blass are present here, except with the addition of a few contemporary pieces, which all melds into and a well-edited, "collected look" without the usual collected-look clutter!

(Source: Waldo Fernandez)
White painted walls replace the ubiquitous striped foyer wallpaper, and a simply accessorized George IV center table replaces the formulaic: chest-lamp-pair-of-hall-chairs schtick.

(Source: Ellen deGeneres & Portia de Rossi)
Two lesbians have the most beautiful 'casually handsome' space in this missive on handsome rooms - go figure... The lounge in their horse barn is without all the typical equestrian gimmicks; unpretentious, worn furnishings supply the comfy-lets-hang-out-y'all vibe.
(Source: Alex Papachristidis)
A modest foyer gets a punch of grandiosity with a few antiques (from several periods) and a kick-ass, two-tone chevron stained floor.
(The old Roman prints of naked dudes doesn't hurt either...)

(Source: Birch Coffey)
A country cottage ditches the tired-ass gingham curtains, rag rugs and pine furniture for a few handsome statement pieces - ergo replacing cute with calming.

(Source: Joseph Paul Davis)
Yacht interiors usually look like discotheques or nouveau riche versions of an Englishman's library. Here, the sea views to override the quiet, tailored interiors.

(Source: J. Randall Powers)
Each piece in this room is part of a puzzle.
And, like a puzzle, there are no redundant, or superfluous pieces.

(Source: Bates-Corkern Architecture)
A graphic carpet mixed with clean-lined furnishings and a simple palette create a contemporary version of 'handsome'
Some trendy piece of furniture, or, yet another, Warhol silkscreen would take this from handsome to boredom...

(Source: Unknown)
This home exemplifies 'updated traditional'
Clean lined, appropriate architecture punctuated with bold art and English furniture.

(Source: Kristen Buckingham)
Random furnishings floating around in this heavily beamed room feels solid and forthright; there's no unneeded curtains, carpets or textiles, only pure, honest materials like leather, sisal and linen.

(Source: Waldo Fernandez)
Fernandez has always successfully achieved "handsome" by combining light-and-airy with warm, dark furniture and honest, almost primitive textiles.