Pastel or softer colors look better in flat paint. Chocolate brown or very dark colors, I think look better with a little shine to them. The satin or semi finish will keep them from looking dreary by reflecting light around the room. Painting is the most cost effective way to give your room lots of impact. You may want to select a striking wallpaper pattern in keeping with the color scheme of the rest of the home. Stripes are great for adding volume and height.
If you choose wallpaper with lots of pattern, you will have very little need for pictures or artwork. When choosing wallpaper, don’t assume that a small foyer should be papered with an equally small printed design. Some of the prettiest foyers I’ve been in, were small ones, where the paper chosen was large scale and very bold. The effect was wonderful! The entry is the perfect spot for tromp l’oeil. Possibly a mural of a Grecian urn or a large topiary.