Here is a link to a pretty good video that explains the principles, different types and operation of geothermal heat and a/c.

I put in a system last year in WI and love it.  The key is the initial design. That starts with how much capacity do you need which is closely related to how well insulated your house/windows/doors are and how large a house it is.

The folks that put my system in say that in the north, heating, rather than air conditioning, is the critical design criteria.  They sized the number and depth of drilled holes to provide geo heat down to an outside temp of -20 degrees F.  They also do trench systems but those were not feasible on my rocky hillside.

My heat is all in-floor and in a new house I would suggest that if you can do it, at least in the basement.  The A/C does require standard duct work. Most folks use the duct work for heat also.  The thermometer on my Water Furnace unit which indicates the temperature in hot side of the ground water loop generally reads 90-100 deg F when the heat is running.

My geo unit has an optional loop in it that preheats the well water going to the domestic hot water heater. The geo takes the water from about 50 degrees up to mid 90 degrees so the hot water heater only needs to take it from about 90 to 120 degrees. Saves about half on the hot water energy required and cost.

While my heat is in the floor the A/C goes through the ducts and the variable speed fan just runs continuously at very low speed and air flow. I suspect if heating through the ducts the same would be true. A lower warm air temp than say a gas furnace but runs more continuously. In that case the room temp would be more uniform and not up and down.

Again the key is getting the system designed properly by an expert to begin with. You want someone who has done a lot of these before, not the low price bidder.  Lots of geothermal horror stories out there too.

Good luck.

Jim at Dawn