We've talked a lot about color this month, and when picking a paint, the hue certainly stands out as the main consideration. But once you've got a color, there's still that pesky question of sheen. The difference between a flat paint and a high-gloss paint is probably clear, but what about the difference between eggshell and satin? And which works better for your needs?
Flat: (0 to 10% gloss) Primarily used for wall or ceiling paint, flat finishes don't reflect light, so they're perfect for masking wall imperfections. Flat paints are also more difficult to clean than other finishes, so it's best to use them in places less subject to mess (bedrooms, dining rooms, etc.). Kids and pets don't always mix well with flat finishes.
Eggshell: (10 to 25% gloss) Eggshell paints have a slight sheen and reflect a bit more light than a flat finish, but are not highly reflective. They're easier to clean than most flat paints, and slightly more durable, but not as durable as a satin finish or semi-gloss. This is a good choice for walls.
Satin: (25 to 35% gloss) Satins are sometimes lumped in with eggshells, since they also have a light sheen, but they are slightly glossier than an eggshell finish. The subtle reflective qualities give walls a silky finish, adding just enough light to add a slight glow. Since they are durable enough to withstand most dirt and cleaning, they work well in high-traffic rooms (kitchens, bathrooms, kids' rooms, etc.), and can also be used for trim.
Semi-gloss: (35 to 70% gloss) Semi-gloss paints go on smoothly and have a nice gleam without being incredibly shiny. These paints are great for window casings, molding, baseboards, doors, and other trim. They're very easy to clean, and rather durable.
High-Gloss: (70% gloss and higher) High-gloss paints will give your walls a shiny, lacquer-like finish. While these paints can have quite a striking visual effect, they will betray your wall's every imperfection, so properly preparing the walls for a high-gloss job can be arduous. That said, these finishes are very durable, easily cleaned, and make quite a statement.
In conclusion, here are some basic considerations to help you figure out which finish is best for your needs:
• The texture of your walls. The flatter the finish, the less the paint will show imperfections.
• The light and space of the room. Flat finishes can help walls visually recede, and the color can appear deeper because of the low reflectivity. Higher gloss paints will be much more reflective and will help light move around the room.
• What kind of wear, tear, and cleaning the wall will undergo. The higher the sheen, the easier to clean.
(Images, left to right: Elle Decor & Jeffers Design Group via DesignWali)

Shaw's Original Fir...
Ohhh that high gloss wall is pretty. My last apartment probably had satin paint in the bathroom and I hated it!!! My hair would literally cling like crazy everywhere! I had to go in and dust the very top of the walls because moisture+dust+ clingy white wall= dirty.
Wow that glossy wall is unusual and gorgeous
Wouldn't it also be wise to consider how soon you'll want to repaint? My understanding is that high gloss and even semi-gloss are hard to paint over without some sort of treatment like sanding or an adhesion primer.
I've found Benjamin Moore paints in the matte finish to be as cleanable as satin. And I have dogs, teenagers and a toddler. We used matte on every wall in the house except the bathrooms, where I chose satin, which I hate. I much prefer the rich velvety look of a matte, especially when using a dark color paint.
I really hate flat finish. In my last apartment there was really only one reasonable option for where to put the garbage and recycling and the wall behind it had a flat finish. It was never clean and it looked so bad.
Where does "light gloss" fall on the spectrum? Valspar offers both semi and light gloss and I was never sure which was which.
Our previous homeowner made a mess of the walls with bad, lumpy patch jobs. I painted a wall a deep red color in eggshell, but somehow the slight bit of reflectiveness showed every flaw in the wall. I've used eggshell in lighter colors and didn't have that problem at all. So take into consideration the color, for sure!
I'm not sure about a "light gloss," but off the top of my head, I know that they have something called a "soft gloss" that seems to fall somewhere between a satin and a semi-gloss. Different brands have slightly different ways of breaking this stuff down, and it gets rather confusing! Hope this helps.
worth noting, a few of the big box stores now carry something called "flat enamel" which is in between flat and eggshell. not quite as chalky as flat with a touch of sheen to aid clean-ability.