Speed in turn-based games is a rather heavily abstracted concept. This isn't a big surprise in Roguelikes which are effectively defined by abstraction. Still, I think speed in Roguelikes has a tendency of being unusually spoilery for something that is relatively significant. This is because the way speed works is rarely something that is spelled out for the player and must instead be inferred through gameplay.
Many Roguelikes that implement a speed system for movement essentially just make it so characters lose or gain a free turn based on relative speed differences. For example, in Dead Man Walking, a character with a speed value of 20 will get to move twice per single move of a speed 10 character. Some Roguelikes choose to take this even further and include numerous, less obvious speeds (like the difference between speed 11 and 13). Some also choose to incorporate an element of randomness into the movement (Dungeon Crawl Stone Soup).
In general I do not have a problem with speed systems in Roguelikes as a player. But, as mentioned, I do find them to be relatively spoiler-y in many cases (i.e., understanding them fully requires external assistance). This is especially true if the game uses the aforementioned granular speed differences and random speed boosts.
One of my goals with Dungeon Brawl (the now-official title of the new project) is to avoid unclear mechanics. Movement and positioning meant to be very important. In my mind that means a speed system designed for it would need to be so complex that it demands spoilers or so insignificant that it might as well not exist. Or it could instead be redesigned to become a much more explicit concept that also conveniently fits the theme of fighting games pretty well.
The speed system in Dungeon Brawl is effectively an abstracted form of acceleration. Characters moving in a single direction for several turns will begin to move two tiles in that direction. Currently this just applies to player characters, though I intend to expand to apply it to enemies soon. The basic idea here is still the same as traditional speed systems in Roguelikes, but it is deliberately designed to function on a much more interactive level.
In my (limited) playtesting thus far, the acceleration system offers a lot of intimate tactical decisions. For example, I might run into a room with full momentum. Now I have to face the decision of whether to keep that momentum alive or switching directions to improve my position or aim at an enemy. This is a fairly basic example, but hopefully it's clear how the new system can have definite applications in regards to how to retreat, how to approach enemies, and just generally how to engage in combat.
As a teaser/example, here are the basic characters' "minimum momentum" scores:
Fat Mac: 3
The number refers to the number of turns a character needs to spend moving in a direction before they start to move two tiles per move. The "last direction" arrow I showed off in a previous post will update to show when the player has surpassed that point (compare above, bottom left of the screen).