Pretty much everyone thinks walk-in closets are a luxury. You don’t have to say anything more than it is a walk-in closet for it to be considered a perk.
Sometimes, walk in closets don’t have as much hanging space as the closet in the next room that is simply a flat closet. The corners of the walk in often are not great usable space. What the walk-in does have is the feeling of space, empty space, it’s another room so to speak.
I think one thing people really like on walk-in closets besides the assumed luxury of space is it has a “real door” rather than bifold or sliding doors. People perceive that as more luxurious too. It looks visually more upgraded. The real door also often means more wall space for artwork or furniture.
In a brochure I’ve never seen someone mention the closet doors on a closet, or the wall space in a room, but you could mention all the doors if they have some sort of upgrade. “All doors 8’ six panel doors.” Something like that.
For the closets I’d just add an adjective:
Luxurious walk-in closets.
Large walk-in closets.
Spacious walk-in closets.
Walk-in closets with extra shelving. (And just add an extra shelf). Or, advertise extra hanging space, and double hand part of it. You can use the inexpensive wire shelves and bars. Most rentals just have the one shelf/bar combo.
If it has deep shelves for a linen closet that’s a big plus for me. 20” deep on one side for large items like bed comforters and blankets. Some markets just don’t think of that.