From an aesthetic perspective, I do not like tanks without a background. This is best if it is dark, whether a subdued picture/design or just plain black construction paper. Anything too obvious, such as bright colours, metallic, glossy photos, etc. will distract the viewer from the fish and plants. Both fish and plants will look better with a background that you don't really notice when looking at the tank. The background also hides the external filter tubes and the cords from heater, light and filter.
As for light, unless the tank is in front of a bright window, this light is unlikely to be sufficient for plants, but it will be enough for algae. If it is bright enough for the plants, they will grow toward it, which can ruin the front view as I found out with an experimental 10g using window light.
On the fish, there is a lot of evidence that they can be stressed by tanks open on all sides and particularly if there is movement on all sides. This varies from tank to tank and fish species to fish species, but I have certainly found a difference with fish response in tanks after installing a plain black background. The fish do seem more "relaxed," though I would find it hard to explain this in words. It's one of those things you just notice, or don't notice.
It is true that fish can usually adapt to movement, and again this depends a bit upon the fish species. Wild caught fish that have come from a densely-shaded forest stream are going to be anxious in a sparse tank; what they need is missing, and instinct tells them they are in danger because of it.