When Mary and I evaluate a game, one of the first things we look at is the Sequence of Play. Perhaps the most important part of understanding a game is understanding what a player does on their turn. It doesn't mean that we're looking for anything really ornate, or fancy, or different for the sake of being different - we have published, and will continue to publish, games that stick to "Player 1 Move, Player 1 Combat, Player 2 Move, Player 2 Combat" - but it does mean that we're trying to get a sense of how that turn is structured, and how that structure impacts the play of the game.
If we get a set of rules that don't have a Sequence of Play, well, that's a big red flag. Either it means that the designer hasn't taken the time to organize the ruleset properly - not a mortal sin, just a really annoying one - or it means that he or she hasn't yet figured it out - which means that it's not a game yet, not by a long shot. (You'd be surprised how often this happens, and that's the reason why so many publishers stress that they're looking for "finished" games.)
So, what, precisely, are we looking at when we're looking at a Sequence of Play? There's a few different things, but the most important is just trying to get a sense of how it plays and how complicated it is. (For the same reason, the second thing we tend to look at is the Combat system.) Broadly speaking, you can divide up Sequences of Play into a few types or categories, and today I'm going to be talking about some of the most common types.
The most prevalent type when it comes to wargaming is a Game Turn, which itself consists of two Player Turns, each with their own discrete Phases. These Player Turns are often bookended by one or more administrative or shared Phases at the start or end of the Turn.
For example, John Gorkowski's Plan 1919 has twenty Game Turns that each consist of an Allied Player Turn and a German Player Turn. Each Player Turn consists of the following phases: Ground Movement, Air Combat, Ground Combat, Exploitation Movement, and Exploitation Combat. Before the Allied Player Turn, there is a Replacements Phase and a shared Alternating Air Moves Phase, and after the German Player Turn, there is a Return to Base Phase for Air Units on both sides.
This particular type of Sequence of Play is ubiquitous in part because it's so easy to understand, basically conforming to "I do all these things on my turn, then you do all the same things on your turn", and in part because it's the one that powered the earliest commercial wargames. The disadvantages of this is that when one player is resolving his turn, his opponent is twiddling his thumbs, sometimes for several minutes. Reaction phases (usually sandwiched between the active player's movement and combat) are one way to mitigate this, but another option is to embed tiny little micro-decisions for the passive player within the active player's turn. Things like opportunity fire (which I'm not actually a big fan of), choice of defensive stance (see, for example, Brian Train's excellent WWII games using an attacker-defender matrix), etc.
These sorts of little curlicues aren't necessary when the Player Turns are very short. Which brings us to our next model, which uses Impulses or Activations to drive play. In this method, each Game Turn consists of a series of Impulses: short player turns in which only a small portion of the player's forces are able to move and/or complete combat (and/or some other type of action). The precise number of Impulses can be defined in a variety of ways. It could be that once every unit or formation for both sides has activated once, or has exhausted its ability to activate, that the turn ends (that's what's being used in my new Shot & Shell Battle Series). It could be that the turn ends when both players pass consecutively, or a certain number of times. Perhaps there is some maximum on the number of Impulses that ends the turn once reached.
You often see this kind of turn format in chit-pull games, with the chit being pulled determining which units activate (and sometimes, what they do when they activate). There are games like Blood in the Fog where each player has their own chit cup and they alternate activations, and then there are games where all the chits are in one basket so to speak, which can result in one side having two or three activations in a row. In the latter case, it's common to have some kind of End Turn chit that will end the turn.
It's pretty elementary stuff, but the thing I want to highlight is that when you use this kind of Impulse format, you need to have some kind of mechanism in place as to how that sequence of impulses comes to an end. And that turn-end mechanism is going to tell me a lot about how the game plays, and what kind of things I can expect. It's also going to tell me how much thought the designer has put into the scale of the game. For example, a chit-pull mechanism that powers a grand strategic level game may or may not be a great idea, but a turn-end chit really feels inappropriate for that scale.
Related to both these models is a model that doesn't use formal Game Turns, but rather an alternating series of Player Turns, with no bookended Turn End phases. These are more appropriate for games that don't use a strict time scale, and that don't have a time pressure element ("complete this thing before this turn to win"). The players just alternate taking turns until one of them wins.
Because there's not a formal Game Turn encapsulating paired Player Turns or Impulses, it's possible for there to be an unequal number of turns. I think this should be taken into account when creating and balancing the game end/victory conditions. It's why, for example, in my Shields & Swords II series, which uses this sort of Sequence of Play, each player checks for victory at the end of his opponent's turn. At least one of these victory conditions is often two tiered, with the lower tier requiring the player to not only hit a certain VP threshold, but to exceed their opponent's threshold by a certain amount. This means that the opponent will have a chance to close the gap.
The structure of each Player Turn in the S&S II games is somewhat free-form, in that the acting player decides which Phases he will perform. So, maybe it's a Move and Combat turn, or Shield Wall and Retreat, or some other combination of the possible phases. This approach - "choose a type of action to do on your turn" - is another way to approach a Sequence of Play, and it has the advantage of keeping each turn relatively short. It's something you see a lot in Impulse-style Sequences of Play; I used it in Blood in the Fog, a chit-pull game in which you choose one of three Phases (Move, Combat, or Charge) each time your division's chit is activated.
There's one more Sequence of Play I want to talk about, and that is what I would call a Procedural Sequence of Play. In these sorts of games, a Game Turn consists of several Phases which are performed by each player either simultaneously or in tandem. That is, everybody does phase one, then everybody does phase two, then phase three, etc. Some of these games can be quite involved; Revolution: The Dutch Revolt, by Francis Tresham, has twenty distinct phases in each of its Game Turns. These phases are often very short and incremental and, well, procedural. It can lend a certain opaqueness to the game, as it can be difficult for players to see how all the pieces fit together. You see this style showing up more often in multi-seat pol-mil games, as it's an easy way to handle multiple players and complex mechanics. It's certainly easier than giving each player a full player turn, as it might be an hour or more before it comes back to you, which to my mind is not ideal.
So, those are some different approaches to Sequences of Play. I think the questions that all of these take into consideration are: How long is it going to be before the other guy gets to make a decision? How long is the game itself going to be? How appropriate are these mechanisms to the scale and point of view of the game? How does the Sequence of Play dictate the victory conditions and the ability of the players to act and to respond? These are the questions I ask when I design a game, and the questions we ask when we're looking at another designer's game.