What does the presence of a door mean? Well, to put it simply, it implies that there’s something behind, a place that needed to be separated from the rest, a place in needs of privacy/security. It tickles our curiosities in a way that no other art asset can, and because of that, they tend to be unintentionally misused.
For example, the most common misuse is the overpopulation of sealed doors. That is, doors that are there to provide “believability” and “immersion” but ultimately frustrate players to no end because they can’t be opened. Everybody hates them! And you should, because they are a symptom of bad game design and bad level design.
In my book, this mistake is the less benign form of invisible walls: It’s an obstacle, essentially a wall that doesn’t communicate to the player “you can’t come through here”. It’s the same as a desk blocking my way, or a little, apparently impassable, hill. Since they don’t communicate their nature to the player, he/she has to try and interact with it first to discover if it’s passable or not.
The worst possible scenario would be to have hills that can be climbed and hills that can’t, but have them both look exactly the same. Sounds silly, doesn’t it? This only confuses the player and forces a trial and error approach on where to advance. The player may even start to question all the things that your game carefully tried to teach him/her.
Well, yes, it sounds silly, but it’s the same exact thing with sealed doors that look exactly like proper doors. And we see this problem all the freaking time.
GTA (Vice City at least) may be one of the worst offenders, but they inadvertently made the sealed doors different than the normal doors by making the former a rather obvious texture on a wall. Flashforward a few years later aaaand… now we can’t figure the difference between one and the other. For once, advancement in technology does not equal greater games, in fact it’s quite the contrary. But I digress, there’s an easy way of solving this issue and I’m more than surprised that I haven’t seen it implemented as often as it should. Tsk-Tsk.
At this point, the solution should be fairly obvious but apparently it bears to be put as bluntly as possible: Make it so that obstacles look like obstacles. When you need to populate your city with houses/buildings that the player is never going to enter, do it, but first make sure to teach the player which ones he can enter and which ones he can’t. This can be accomplished with a minimap showing this vital information, but there are more subtle ways of doing it.
For example, you could make two types of visually distinct doors. One that opens and one that doesn’t. Then, even if you don’t mention this fact to the player, he/she is going to notice sooner or later. The same goes for breakable and unbreakable scenery: Make them visually distinct (ya hear that half-life 2?). It’s not that hard, you know. It’s a very simple language that communicates vital information to the player just by having different visual patterns for obstacles.
What about invisible walls, then? What about them indeed, there’s a simple solution to them and I’m proud to sum it up in just three words: Better. Level. Design. Thankfully, invisible walls haven’t been much of a problem in the last few years, so at least that’s one problem solved. In general, we still have a lot of room for improvement though.
Oh, and if you want to read more about this subject be sure to read this fantastic article on Gamasutra. (The Battlefield 2 and CoD4 images come from there)