A fun challenge for any designer is to try to make a "paper" version of a game where it seems impossible. For example, a version of Dance Dance Revolution or Super Mario Bros that is played with cards or boards or dice.
Probably the hardest part of this is getting the same fundamental feel without the physical skill play. You can substitute in another kind of skill play (such as memory in place of timing), or you can try to come up with a mechanic that produces the same dynamic and feel as the skill play by other means.
For example, in first-person cover-based shooters such as Mass Effect, Halo, and every other FPS made in the past five years, there are a lot of highly polished game mechanics reused and recycled to produce the same dynamics. Fundamentally, we might consider firing (accuracy and DPS), exposure (timing and concealment), tactics (flanking, prioritizing targets, maneuver), and resource management (ammo, health, powers, squadmates, etc).
So you can start to break those four into basic relationships. If you want to fire on an enemy, you need to break cover. So you inflict a certain DPS at a certain accuracy, while paying in exposure. You will probably wait until fire dies down (enemy reload, for example) before popping up, to minimize the actual chance of getting hit.
Maybe you want to reduce exposure even more, so you maneuver to an area surrounded by pillars. Now you pop cover to fire on an enemy, but the pillars are still between you and the other enemies, meaning that your exposure is limited.
A rocket launcher has a long reload speed. It probably has roughly the same DPS as an assault rifle using naive calculations. But you can reload while in cover. So the rocket launcher fundamentally has a super-high DPS followed by a required reload phase - which is a different class of cost. So "DPS" must be calculated by "seconds exposed", not "seconds including reload time".
A psychic throwing magical balls of tracky force has a similar issue, where he may not even have to break cover to fire the magical balls, and then they home in or are piloted. Again, a very low level of exposure and, often, a very high effectiveness against targets who are hiding (goes above/around cover). Largely balanced by the low level of damage and the long recharge time, but it may be the reason why I feel that the most powerful class in Mass Effect was the pure biotic. Those long recharge rates don't matter much when you don't ever have to break cover.
That can backfire, though, if the enemy presses and you have no place to fall back into. Cover can be broken by an enemy simply flanking or even flat-out entering melee. A biotic has relatively poor direct survivability, so when they lose control of the tactical situation, it goes poorly for them.
I'm thinking it could be fun to theorize a simple tabletop game like this:
Cover is a resource. Fundamentally, it is shields - the more cover you have, the less the enemy will be able to damage you. However, you must reduce your cover to fire upon the enemy. You can gain cover by maneuvering or destroy the enemy's cover by maneuvering against them, but either way requires you to temporarily reduce your cover. This is called a "tactical maneuver".
Position is a resource. The better your position, the more effective tactical maneuvering is, and the less effective your enemy's tactical maneuvers are. Also, the better your position as compared to your target's, the less exposure you need to fire on them. Position can be gained by a different kind of maneuvering ("strategic maneuver"), but this is often limited by the realities of the terrain. If you're stuck on a veranda and there are airships firing on you, your position is not going to improve.
From those two resources spring the majority of the dynamics of our tabletop game. After that it's secondary resource definition. Here's a sample of how you might define a character:
Health vs speed. What is your bonus to maneuver vs your durability?
Size. Smaller means more effective cover, larger means more effective melee.
Rocket launcher. Upside: Low exposure, high damage. Downside: expensive, heavy (reduces speed).
Assault rifle. Upside: Reasonable DPS, variable exposure to fit your tactical situation. Downside: No exceptional stats.
Pistol. Upside: low weight (no speed penalty), low exposure. Downside: low damage.
Ghost. Can momentarily vanish, allowing for tactical maneuvers without exposure.
Psycher. Can lob energy balls which flush out the enemy, bypassing cover.
Traceur. Can make a tactical and strategic maneuver simultaneously, but only wears the lightest gear.
Commando. Can attack while making a tactical maneuver.
Cyborg. May fire two weapons at once at only the exposure cost of one.
Etc, etc, etc.
Could be fun.