FPS Level Design (Single-Player)
Introduction
FPSs are a breed unto themselves, and require a particular kind of level design. Whether your game is a 'run and gun' or a tactical, thinking-man's shooter, chances are your level will have things common to other FPSs levels - or at least, considerations.
Level Structure
There are a couple of overall level structures that you can consider for your level, some are easier to make 'half decent' than others, though all can be done well.
The Hub
The Hub, is a style of level where you return to a particular area more than once during the course of the level. It will probably have branching areas off this central hub space, these may be sealed off initially, or you may leave them open for the player to explore. Note - there is a difference between a true Hub level, and one that just happens to have lots of non-essential branches. A true Hub level will require the player to revisit the area more than once.
Example of 'The Hub'
From the central hall of the pyramid, explore the three crypts and bring back the three fragments of "Ra's Sun Disc" to open the underground chamber of the Mummy.
Here, you have the central chamber being the 'Hub' with four offshoots - one is sealed from the player, but the other three may be entered at any time.
Pro's
By reusing geometry (level space) you can get a lot more play time out of a smallish level because you backtrack.
You can mix it up by having areas you've already visited change on further visits - maybe a pillar collapses, or zombies break down the doors.
You can give the player a 'base of operations' at the Hub point, somewhere to stash or collect ammo and other pickups.
Con's
It can get dull - players like to see new stuff, so unless you're careful to add changes, or change the way enemies attack while you're backtracking, they can quickly get into a "Seen it before" mentality.
Care must be taken to avoid a specifically "Collect three items" syndrome as seen above. Unless that's how your levels work, of course.
Linear Levels
A Linear level is one where the player goes forward all the time. The level, though it may make many twists and turns, never actually branches and if stretched out, would be a straight line from start to end. There's no backtracking, no choices of which way to go, and no real thought required.
Note, however, that Linear levels may (and should aim to, for vertical interest) loop back on themselves to see where they've already been - good examples being fighting through a canyon, up through a cave system, then across a bridge you went under earlier. It's still a straight line, but it's always nice to see where you were, from a different angle.
Example of 'Linear'
The Sergeant needs you to fight through the trenches, blow through the barrier on the other side and secure the bunker for the dropship to land next to. The only way is onwards!
With trenches providing a simple 'corridor' for the player to make their way through, even blockages can be gone around by going through simple bunkers and rooms off to the side. It's still a simple path all the way to the bunker at the end - the corridor just looks different.
Pro's
Easy to do - this is probably the simplest kind of level to do reasonably. Pick your challenges that you want to throw at the player and arrange them in a line - then twist that line, add some interesting geometry and you've got a level.
You can do lots of 'one shot wonders' with level events - collapsing bridges, exploding statues, crashing spaceships - you know which direction the player is coming from, so you can set these up to be superdramatic.
Con's
Can seem restricting. Modern gamers are getting very wary of linear gameplay - they don't like it. But if you do it well, they might not notice. HL2 was linear, but their 'corridor of gameplay' was so well hidden that most people never felt restricted.
No reuse of assets. Players don't get to learn an area, they are always new. This is both good and bad. It's expensive in level building terms - it's cheap to just use the same level parts over again
Branching Levels
The branching level has several ways to your objective. Maybe one way is a stealth way, maybe one requires explosives, maybe if you keep your AI buddy alive he'll open a door, maybe "You take the high road and I'll take the low road". Whatever way, branching a level gives options to the player and depending on the strategic worth of those options, may cater the gameplay to their style.
Example of 'Branching'
"Here, listen up - if you want to get into the castle there are two possible routes: you could try to get in through the front gate, even though it would be suicide, or I hear that there's a secret tunnel through the moat and into the kitchens. Of course, you'll have to actually get TO the castle first..."
In this scenario, the player gets the option of a frontal assault (and told that it'll be hard) or told that there may be a sneakier route available. Some players will jump at the chance of a big fight, whereas others will prefer to stealth in. This means that you can be really vicious on the frontal attack, and really really sneaky on the stealth approach. Because that's what they've chosen, and that's what they're expecting.
Pro's
Lets the player feel clever - if there's a secret entrance, or a stealthy way, or even just a not as obvious path, the player will feel smart if they find and use it.
Lets you cater the gameplay to their style - they 'choose' the type of gameplay, so give it to them!
Keeps it interesting, and choices are almost always good. Avoids dreaded 'linearity'.
Con's
Harder to balance. It's not as easy to ensure that both (or all) paths are as challenging - if you have one path harder, make sure there's goodies or another reward for the player who takes that route.
Some geometry is 'lost' - the average player, who plays your level will never see the other path. They'll never see the pretty graphics, your cool effects, your funky eventy. It's heartrending, but it's the way it is.
So there's the three simplest level types - some others are 'The Arena' - where it's pretty much one big area with many fights (drop your enemies in where the player can't see them), 'The Web' - kind of like the Hub, but your player works around a central area and only gets in when they've completed an objective, then gains access to all the previously visited areas.
Also, you can probably see that a lot of these will work with other genres - platformers in particular are fond of Hub levels and Branchers, while Crash Bandicoot was pretty much all Linear levels.
Once again, I hope I've helped, not hindered and I
really hope I haven't preached
