Essentially, I'd like to imbue a straight up board game, like Descent: Journeys in the Dark, with a bit of the character building and advancement I enjoy in D&D, without the rules exceptions and complications that bog down play.
I feel there are a few common elements that tend to slow things down.Any further input would be appreciated.
1a. Conditional modifiers to stats, rolls, etc. that cause you to calculate your totals repeatedly during the course of play.
1b. Special situations that require extra rolls or calculation
2. Actions that do not happen on your turn (counter attacks, dodge rolls)
3. Too many options to choose from
4. Too many actions on one turn (including the game master)
#1a/b are common in 'realistic' RPGs, where every roll is unique to the situation. Incremental modifiers for range, attack type, cover, and motion means you need to do math every time you wish to act. Of course, floating +1's and conditional modifiers are common in almost every encounter-based game.
In D&D, the Rogue sets a good example for speeding up play. He either gets his sneak attack dice or he doesn't, requiring no situational calculation besides setting them aside when they are not necessary. A simple arithmetic bonus is also easy to manage, but the more complicated the system gets, and the more modifiers that need to be added up, the longer each person's turn takes (because even in a room full of smart people, players will find the need to sit and count their additions out one by one every time, especially if they're factoring bonuses for charging, or fighting defensively, or whatever).
An extra dice dynamic, such as 'roll one extra blue die on a precision attack' is a practical solution. If it was coupled with a way to keep track of what dice you have--using cards, for example--then you have a simple visual calculation to decide what you need when you roll. And if a target ignores a certain attack type, you could, for example, ignore rolling that die when you take your action (Assuming you've got dice that determine the chance and degree of success).
#2 doesn't necessarily hamper play very much, but even one reactive roll/decision (like making a parry roll) can interrupt your thought process and get you back to square one; if a player's turn is the only time they won't be interrupted, when it comes around, they will waste time by completely reevaluating the situation. Therefore, avoiding reactive decisions as much as possible would be ideal. E.g. Marking off a few lost hit points is a lot less distracting than having to decide whether to use a limited defensive ability, totalling various bonuses, and determining the outcome of that decision.
#3 is a big deal, and part of streamlining a system would be to figure out how much you can limit a player's actions without limiting their decision-making, and therefore enjoyment. Spells in almost any game are a good example of how too many options can kill the momentum of an encounter (for the players, at least).
Perhaps the goal should be to 'discipline' a player's options instead of 'limiting' them. The job system in Final Fantasy Tactics was an elegant way to keep options open for the player but also speed up the gameplay. Keeping a character's options open but disciplined still lets characters make important decisions about their character's actions, but moves some of that decision-making time to the open period between encounters, instead of slowing down the game on each and every turn.
Forcing characters to a smaller array of options could also emphasize 'niche' roles, if that's your bag. For example, in contrast to Tactics, Final Fantasy 12's skill system was set up so a high-level character could pretty much do everything whenever, which meant all of the characters felt pretty much the same after a while.
#4 is closely related to the above, but is more basic. If any of the players has to perform multiple actions on their turn, it slows the game down. The Game Master, for example, often moves and acts with a half-dozen or more different entities on his turn, or takes multiple turns during every game round. Even though those moves have an impact on the choices of the players, waiting as the GM rolls a dozen sets of dice and asks for different information from each player can be a drag. Ideally, it would be nice to simplify the game enough to make being the GM as complicated as being a player.
Of course, they're all related, and a lot of it has to do with simply "How much can a character do on any given turn?". I've got some ideas about that, like moving and action orders, that I might hold off on for now simply because I'm sick of typing this entry.