Matapalo, not to be confused with the other 2 Matapalos in Costa Rica, is halfway between Quepos and Dominical on the Coastal Highway, which here leaves everything to be desired. It is unpaved, potholed, has no signs or directions, and goes down to one lane at bridges or maybe the bridge isn't there. It is passable, however, and it takes an hour to go the 20 km from Quepos.
As a result it is utterly unspoiled. Has a few bed and breakfasts and some world class restaurants because people have moved here and need to support themselves, not because there's lots of tourists or high rise hotels.
The road after Quepos is like nothing you've ever driven. Potholes, one lane bridges, dust, things on the road that pass for vehicles, people walking on the road, etc. Make sure your vehicle can handle it. You don't need 4 wheel drive, but it's good to have if only for the higher clearance.
Don't let this stop you, go anyway..
Update December 2011
I am headed down again, in two days, and this time I hear the road is paved and the bridges are really there now. Should make a big difference! So now you have no excuse not to go!