what i love about pandemic is that each player role represents a major exception to the rules of the game. it often turns out for me that playing one game, and then another right after, feels really difficult because if anyone decides to change their role, you have to completely rethink your strategy for how to win the game.
to show what i mean, i’m going to give a short explanation of the game’s rules, and i’m going to follow each rule with a role description that basically overrides it.
rules (and roles) of pandemic
at the beginning of the game (and after each player’s turn), cities across the world are randomly infected with disease. you draw a card from the infection deck to determine which cities are infected. the goal of the game is to develop cures for all 4 diseases.
disease is represented by little colored cubes. each city can have up to 3 disease cubes. if you would have to put more than 3 cubes on a city space, you instead put one cube on each adjacent city. this is called an outbreak.
QUARANTINE SPECIALIST: whichever city the player stands on and in any adjacent city, there cannot be any new disease cubes placed (including from outbreaks).
players can make 4 actions each turn. for example, players can spend 1 action to remove 1 disease cube from a city. this reduces the chance of an outbreak, and also prevents the lose condition that you run out of disease cubes to place.
MEDIC: remove all disease cubes from a city; if a disease has been cured, remove 1 cube of that disease from any city you walk through without spending an action.
players can also spend 1 action to move their piece from one city to another.
DISPATCHER: move any other player’s piece as if it were your own.
at the end of a player’s turn, they must draw 2 city cards. they must accumulate 5 cards of the same color to cure a disease at a research station (1 action).
SCIENTIST: you only need 4 cards to cure a disease.
you must also spend a city card to build a research station in that city (1 action).
OPERATIONS EXPERT: build a research station in a city without needing that city’s card.
you may give or take city cards from other players to help each other cure diseases (1 action); however, you must both be standing at the city of the card you’re giving or taking.
RESEARCHER: give any card to another player in the same city as you, regardless of the city named on the card. 
sometimes you’ll draw event cards instead of city cards, and you can use these for special one-time effects like building a free research station or skipping the infection deck that turn.
CONTINGENCY PLANNER: re-use each event card once.
i hope you see what i mean! each role becomes super useful because they act as powerful exceptions to the base rules of the game. it’s both really creative and really fun, because it requires you to think about how best to strategize together as a team.
applying to other things
there are two broad ways you can differentiate player roles in a game: quantitatively (different numbers) and qualitatively (different abilities or attributes). dungeons & dragons basically does both, but it tends to rely on the former and then be kinda boring about the latter. for example, magicians are different from fighters because they get to use magic, and clerics are different from both classes in that they use a different kind of magic. thieves just do their own thing.
instead, why not define abilities based on core procedures of the game? like whatever, let's do it now:
- when you explore a room, you have a 1-in-6 chance to find a hidden door if you're looking for it
- ELF: roll to detect without spending a turn (once an hour?)
- when you come across a trap, you have a 2-in-6 chance to detect and then disable it
- DWARF: roll to detect without spending a turn (once an hour)
- THIEF: roll to disable without spending a turn (once an hour)
- when you come across monsters, make a reaction roll to see if they're hostile
- CLERIC: force a second reaction roll to scare the monsters away (once an hour???)
- when you fight a monster, roll to-hit and then d6 for damage
- FIGHTER: attempt to-hit twice or roll damage twice (etc)
- when you cast a spell scroll, you cannot cast it again for the rest of the day
- MAGICIAN: cast any spell scroll twice per day or get two attempts to use it
these are all kinda bullshit but i hope the point is coming across lol. i think part of the difficulty is that the party sticks together in d&d, whereas in pandemic they move independently across the board and make their own actions. another difficulty is that each turn in d&d is less significant by itself (and a crawl can take a lot of time), so maybe you don't want abilities that you can use each turn. but i don't think countdowns are the best way to do that either lol.
would love to know what y'all think!
 when i play with my partner and friends, usually we let the researcher also take cards from other players regardless of the city they're in; maybe this is overpowered lol but it's easier to wrap your brain around.