In the comments on Encounters: A Similar Formula , Ian Toltz of made a great comment outlining three broad types of encounter. His analysis is succinct and useful, and he was kind enough to let me turn his comment into a guest post.
– – – – –
If I may put forth this idea, any story-related encounter in which the party can succeed or fail should come in one of three basic varieties: obstacles, breakthroughs, and climaxes.

Obstacles are encounters which hinder the party if they lose. Many combats would fall into this category, where the party has little if anything to gain from winning and realistically are only fighting to avoid the setback or other general nastiness.

Since there is no reason for the party not to avoid it if they can, obstacle encounters generally are non-optional. Oftentimes, they represent the antagonists’ direct efforts to thwart the heroes, whether actively (an assassin) or passively (guards).

Breakthroughs, on the other hand, are encounters which the party could easily ignore if they so chose without any relative drawback, but they stand to gain if they go through with it. Many skill checks and things like that would fall into this category.

Researching a monster’s weakness, for example, would give the party an edge when they fight it, but if they choose not to or fail they’re no worse off than before. Similarly, attempting to scale a wall to avoid the larger guard contingent at the gate and get in there stealthily would be breakthrough. Oftentimes, breakthroughs are the result of the players being proactive.

Finally, there are climaxes, which are special. While not neccessarily the actual climax of an adventure/session/whatever, climaxes are the “important” fights. It might be a “mid-boss” of sorts, or it might be the big bad itself, but a climax is an important battle in which failure, simply, is not an option.

These are the fights where you pull out all the stops, and where the players have to eke out a victory or all their efforts were for naught. As such, climaxes should be rare, memorable, and fun. In all likelihood, the party should even be expecting them (which isn’t to say they need always know that they’re about to face a big enemy, but they should at least have an inkling that there’s an ancient wyrm hunting them down that could pop up at any moment).

Now, these aren’t hard and fast rules, and there are certainly lots of cases where the lines between them blur and you can even combine different kinds of encounters, but I think it serves as a good set of guidelines.
– – – – –
Thanks, Ian!

I find Ian’s setup intuitive, and he’s spot-on about the differences between these types of encounter. What do you think of Ian’s classifications?