To hide wall imperfections and make a wall more interesting and appealing you need to incorporate some disguise and consider how and what to revamp, embellish and decorate. All this can be done without wallpaper.
First of all consider the wall imperfections and how serious they are as well as the time, effort and money you can spend.
If the wall has fine cracks you can paint over them with an acrylic paint which is often enough to do the trick. Large cracks can be filled with appropriate fillers and sanded back and finished with a flat acrylic paint. Stay away from glossy paint finishes as they exaggerate any imperfections. A more imaginative and creative approach would be to paint a wall mural allowing for the cracks to be part of the picture. As a quick and last resort just cover your wall with a wall hanging.
If the wall is uneven consider applying a textured paint finish. You can create a rough Tuscan' finish or a soft suede effect. Paint effects such as ragging are also a good disguise technique.
If you have a flaky and peeling wall spend some time sanding the wall back and preparing it properly before you repaint. However, a wall that is flaky with peeling paint may indicate a more serious problem than inadequate preparation and the incorrect application of paint. You may find that you have a problem with rising dampness which can be a costly repair job. There may be many reasons why you would prefer to cover this problem up in the interim rather than face a costly repair bill. In this case consider buying and installing a long curtain rod and hang curtains all around. What you hang can give the room a very exotic feel. Add some scatter cushions and you have a very unique and creative space.
Wall hangings can be simply a piece of fabric that have been stretched and framed or hung on a rod; any artwork or a print; a quilt; a large pin board or magnetic board suitable for fixing photos, posters, and anything of interest. A well placed mirror can also work well to take the emphasis off an imperfect wall as they reflect and add interest to an otherwise dull room.
If you are renting a home that has a very imperfect wall a simple way of disguising such a wall is to buy yourself a folding screen and place this in front of the defective wall. This will add interest and take away the emphasis of the wall. When you move out the screen is easy to fold up, take with you and reuse.
Another way to approach an imperfect wall is to take the emphasis away from it by creating something of interest within the room. A vase, a piece of sculpture or flower arrangement on a table makes a perfect decoy for the eye and at night it can be lit to create drama and interest. An unusual piece of furniture set against a perfectly coloured feature wall creates an interesting setting. A colourful rug in the middle of the room draws the eye to it and the wall fades to insignificance. A unique lampshade or light fitting creates an interesting distraction.
Sometimes, we place far too much emphasis on something that in the total scheme of a room setting can be quite trivial and irrelevant. Consider the positive aspects of the room. Does it have a view to the outside landscaping; can you reduce the clutter within the room; if you paint the walls darker or lighter will this help the way you view the imperfect walls?