Cadence
A pattern of beats and rests that describes a recognizable rhythm and creates a sense of repose or resolution
But first, a verse:
Roses are red,
Violets are blue,
Poetry has cadence,
And so should your gameplay.
What a terrible poem! Any second-grader could write a better one. It isn’t the content; if I simply wanted to argue that gameplay, like poetry, should obey rules of meter and form, it wouldn’t offend your sensibilities. The poem is bad because the cadence is wrong. Instead of resolving the contrasts set up in the first half, the second half breaks the rhythm and leads to a jarring and abrupt end.
In the same way, the wrong cadence can take a good game mechanic and make it feel awkward or even abrasive. A gun that fires slightly too fast and ends up degrading into a buzz. A melee combo that is a touch too slow and never feels like it flows smoothly from one hit to the next. The boss monster whose sweeping tail attack is a little too regular, making it feel robotic and gamey.
There are a few basic components to cadence, and usually just taking the time to notice them is enough to know how they should be adjusted.
- Tempo – The speed of a cadence, often described by the number of beats per minute. A good rule of thumb for finding tempos that feel good is to use the same ones found in music. For instance, the rate of fire of the Halo Battle Rifle is almost exactly the same as the BPM of Queen’s Another One Bites the Dust.
- Regularity – Some cadences need to be extremely consistent, like a metronome. The ticking of a clock or the firing of a machine gun sounds mechanical and precise because there is no variance in the cadence. Others need a slightly irregular rhythm, like footsteps or a series of punches. Slight variations in the timing leave a more organic impression.
- Acceleration/Deceleration – Known in music as Accelerando and Ritardando, this describes the way in which a cadence changes from one tempo to another. Very slow changes in tempo create tension, like a train departing a station. Quick changes in tempo will attract the players attention, and are great for helping them to anticipate an attack or other event.
- Style – Some cadences have short, crisp beats (called Staccato), while others feel blended, like pulses (called Legato). Varying the styles of cadences can change the mood or provide contrast between two game elements. Having one gun that fires short, separated bursts of bullets and another that emits a continuous wavy beam, for instance, would allow players to choose their own style, and give them a deeper array of options.
If a game mechanic or other element fulfills its intended role, but still feels unsatisfying or mysteriously broken, try changing the cadence to reinforce and amplify the experience.
Rewarding Play 
(I’ve been waiting for the right post here to share this and I think I’ve found the right one. ;)
There was a piece of research I learned some time ago — unfortunately I read too many books and listen to too many podcasts to be sure where, although if I had to guess I’d say it was on NPR’s Science Friday show — that rhythms with a tempo of two-thirds of a second (i.e. 90 BPM) had a pleasant, soothing effect on the listener.
There were a lot of things that they compared this to (rock ‘n roll and similar styles of music, for example) and I believe the researchers hypothesized that the effect was caused by the similarity between this tempo and the tempo of a pregnant woman’s heartbeat (usually right around 90 BPM, or so they said).
Of course, when I read “Design in Detail” I picked up on the fact that the firing rate of the Halo Sniper Rifle (0.7s, or about 86BPM) is rather close to this tempo as well…possibly meaning that this was another case where that tempo was picked because it “just felt right”.
I realize that “cadence” has a bit wider scope than this, but I thought it might be a useful bit of knowledge to share.
Right on, that connection is so interesting and that kind of sensitivity can take you from an average game to a much more highly polished feel. If you remember where that info was from, I’d love a link. One thing that is also interesting (that is from a source that _I_ can’t remember) is that while very few people have perfect pitch, almost everyone has an excellent ear for tempo. If you play a song back slightly too slow or too fast, people will pick up on it right away. Makes me think that rhythm is imbeded pretty deep in your brain somewhere.
I’ll try to track it down – if it wasn’t “Science Friday”, I’m thinking it was probably CBC’s “Quirks and Quarks”, both of which, I might add, are fantastic weekly resources for the sort of research that can really get stuck in your craw and lead to a nifty insight. And both of which are podcasts you can download for free.
I’ve known a few people who were completely tone-deaf, but never have I met one who was tempo-insensitive. Just from that, I’d say I have to agree with you that tempo is definitely a deeper-seated sort of sensation than tone is. Sort of like how although some people are blind to the color of light, they can still see its intensity (dark/light).
Sorry, no luck – been trying to brainstorm this all day after I hoped maybe sleeping on it would help jumpstart my memory.
Even trying to track down the original study on Google Research was no help, and I don’t have access to any other academic search engines. My best guess is that it was on an older episode of Science Friday that I don’t have downloaded to my current computer, but searching their website gave no matches. Although, it did reveal this rather…well, they describe it as “perhaps the cutest study ever published in the Proceedings of the National Academy of Sciences“: http://www.sciencefriday.com/videos/watch/10289
If it comes to me I’ll certainly post it but at this point it’s not likely.