So I want to make a "hack and slash" where, instead of playing as adventurers on dungeon crawls, players are townsfolk trying to defend and maintain their village.
The setting takes place in the aftermath of a magical war that has decentralized society, warped the landscape, and resulted in the evolution of chimeric monsters that now dominate the ecology. Humans must learn to live with these monsters however, since all the normal flora and fauna died out the monsters are now the only source of sustanance.

The townsfolk must cooperate in order to survive in this strange new world. This requires that the player's characters should fill clearly defined roles in the society. For this reason, the game would use a class system.
Classes in the game fall into four basic categories:
Runner
Extractor
Processor
Maintainer

Runners:
Runners explore the wilderness in search of dangers or resources. When resources are found, they guide Extractors to the site to collect it.
Runners are also good for carrying resources and goods back and forth.
Runner classes include Scouts, Messengers, and Merchants.

Extractors:
Extractors draw out resources so that they can be carried back to the village for processing. Extractor classes include Woodcutters, Farmers, Fishermen, and Miners.
This job is harder than it sounds in this setting.
Trees sometimes fight back when you try to chop them down.
The only vegetables that thrive in this world can uproot themselves and swarm the farmers.
The only fish that thrive are vicious man-eaters.
Even the rocks are alive!
As such, Extractors must fill train in specialized styles of combat in order to do their jobs.
Woodcutters use their axes to chop down enemies many times taller themselves, exploiting their foe's size for added power.
Farmers herd large groups of small plant enemies into an enclosed area so that they can mow down many enemies at a time with weaponized farm-implements.
Fishermen use bait, traps, and lots of patience to catch aquatic enemies.
Miners dig through layers of strong defense to chip away at stone enemies with lots of HP.

Processors:
Once resources are collected, Processors craft the raw materials into useable tools and goods. Processor classes include Carpenters, Brewers, Cooks, and Black Smiths.
Processors must pound and cut away at the materials to make them conform to their desired shape. This is often complicated when enchanted materials collected from the wild are able to spontaneously spring to life. For this reason, Processors serve as conditional combatants similar to the Extractors except that they work in a more controlled environment (their workshops). Processors do this in order to convert resources into food and medicine for healing or tools and equipment to make other townsfolk more effective at their jobs.

Maintainers:
Maintainers are responsible for keeping the other townsfolk safe and healthy so that they can perform their jobs more effectively. Maintainer classes include Deputies, Doctors, Teachers, and Entertainers. They can serve as general purpose combatants in case of unexpected attacks, or they can administer food and medicine created by Processors in the event that an attack does happen, or they can raise morale as Entertainers.

So anyway, players must cooperate and perform the jobs they volunteer to do in order for the village to survive. No ideas about the resolution system or anything yet.
Any comments? Questions? Ideas? Suggestions?

Sorry.

What sort of specific feedback do I need?
Well, what sort of resolution system would you guys recomend for this game?
Would you recomend karma based or randomized?
Could this game work without a DM?

Personally, I think it sounds like a fantastic idea for a game. In terms of a system, it depends on how much you want the game to play like an RPG (versus a one-shot or a board game). If you're willing to let the game be more "party"-ish then I see no problem using a dice pool or cards. Otherwise, I recommend keeping the underlying mechanics simple, even if you want to build more complex rules on top of it.

Again, if you were to go for a less traditional style of game then I would recommend random over karma, particularly very random (meaning an unpredictable dice or card engine).

I actually had an idea for a game that was run GM-less using randomly generated terrain and a constantly switching macro/micro "view" of the game. As a settlement explored its surrounding areas then new geography would be randomly generated, and things would be done on a macro scale. When certain kinds of things were explored, however, the game would switch to a micro scale of the individual players' characters participating in larger conflicts. If you were to do something like this then it might be interesting to see the players working together to run this town, and then zooming in on individual conflicts that occur with these monsters.

- Gregory Zitelli

I can see this game working very well with or without a DM, although without a DM prescripted scenarios or random generation of enemies would be necessary.

I would recommend a very random combat system like Illetizgerg said. This would make things more interesting without a DM (especially since this is a hack & slash).

I like the general premise for this game but just for a rather unhelpful comment/idea/suggestion which is probably too early for this stage of development.

I'd rather not be a fighting class character battling which chimeric monsters but I am actually a "extractor", obviously they are the resource collectors, I'd much rather be a "hunter" if your know what I mean?

But obviously class names to detach this world from the real world are something that you are making later I suspect?

One idea I had was to use a tarot deck to randomly create terrain. Cups would represent bodies of water, wands would represent wooded areas, swords and pentacles would represent mountains and rocky areas, and trumps would represent ruins. Each individual card would have a corresponding 'micro' map in the game book with a recomended scenario.
I was just thinking maybe the initial map creation could be incorporated into character creation. Each player would start out by drawing four cards from the tarot deck. First they assign each of these cards to a square on the world or 'macro' map, then they would assign each of these cards to one of their stats. I'm thinking of using three stats for this system:
Faster (Determines how long it takes for characters to perform tasks, move from place to place, and how rapidly the character can attack during battle.)
Cheaper (Determines how much energy is required for characters to perform tasks, how often the character has to take breaks, and how much stamina the character has in battle.)
Better (Determines how well the character is able to perform tasks, the character's ability to avoid accidents, and how strong or accurate the character's attacks are in battle.)
I'm not entirely sure how to represent these ability scores using tarot cards at this point. What does a three of cups versus a three of swords mean as far as 'Cheaper' goes? For that matter, what does it mean if you have a 'Death' in Faster?

Roadkill:
Hunter is one of the 'hybrid' classes I was thinking about. Hunters would count as both Runners in that they have to seek out prey and follow it, and Extractors in that they have to kill the prey to collect the prey's carcass and bring it back to the village.

I do understand though that some people would rather play as adventurer type characters like 'Sword Fighters' or magical characters like 'Witches'. Now that you bring it up, I think that these should definately be options but I would prefer that players acquire these classes over time. When you start out at level 1, you are only able to choose from Townsfolk classes but when you get up to... level 5 or so, you can start gaining Adventurer classes like Knight or Wizard. What do you think?