Level design involves just as much artistic judgement and compositional skills as any other forms of design. Perhaps even more so. There are many things that have to be considered differently compared to other forms of work and therefore it is slightly more difficult to get composition correct. You have to take into account that this will be a playable level, therefore there are thousands more factors to be considered, because a player can walk anywhere, can look anywhere, so its difficult to know what will happen. You have to think about how certain objects could be interactive, how certain pathways may be blocked for whatever reason. You have to keep them interested in playing the game. For example, if there was a single room and a corridor leading out of it, and then that’s all for that level, you go through the last door at the end and then get a loading screen, that would have been quite a boring stage in a game. So instead, breaking up pathways can make it more interesting, block certain areas and make it an objective to unblock it, either by throwing objects out of the way or finding a key, or blowing something up. You would need to make sure that tasks to be completed are indicated, but also not blindingly obvious. For instance, if a level is quite big, in order for the player to not get lost, you can use light to lead them through the level. Even certain colours of light could mean different things. Objects placed in a certain way, plus lighting can make an area more interesting. It could entice the player to explore more in that place, if that is the desired effect. Perhaps there is something important there to pick up. But at the same time it can’t be too obvious because then there would be no challenge, and that is the main concept of games. They have to be fun and challenging, and a level that has a big sign saying walk forward and go through here would be rather boring!
Let’s say you have made a special side room, with bright blue lights, and they are highlighting a key card on a table, while you may assume this to be enough to lead the player’s eye to that point, but they may not be interested. Depending on where the door to the room is, they may decide not to explore that part, regardless of lights. Perhaps they decide to go a more linear path because they want to get out of this area. And even that feeling of wanting to leave could be down to the composition and atmosphere of the rest of the level. If there was no incentive to explore at any point, then likely the player will not. Another thing that could be more difficult to consider is that what draws one person in, may not draw in another person. But obviously a level cannot be designed to a specific person. Therefore, you have to go with averages and mediums.
Most developers will make alpha versions of the game and have testers play through it. These would be very basic versions, perhaps only whiteboxes of the layout. But this would allow the game to be tested early on, before the rest of the game is put in. It’s a great way to see if you have the levels designed in an effective way. Feedback from the testers at this stage is invaluable.