However, I do recommend getting a 4WD vehicle. Many popular destinations here in Costa Rica require

During our first few weeks in Costa Rica everyone told us NOT to drive, and so we listened.  Then on about our third weekend, we rented a car and drove to the beach, and realized that everyone that had told us to not rent a car were totally missing out.
Driving in Costa Rica is definitely different, but it offers you the freedom to see so much more of the country.  We rent a car almost every weekend and drive ourselves to our destinations.  The roads here are for the most part, pretty nice.  The government just built a highway (27) that connects San Jose to the pacific coast.  As long as you go slow and be cautious of the merges, you will be just fine.
However, I do recommend getting a 4WD vehicle.  Many popular destinations here in Costa Rica require you to drive on a dirt road for at least a few miles, and the experience is much more pleasurable in a larger car.  With that being said, sometimes 4WD in itself isn t enough.  This past week my family came for a visit and we rented a gorgeous house on top of a large mountain in Uvita.  The first night driving there we got stuck in our 4WD vehicle germany rental cars on a very, very steep hill.
Traffic can get really annoying when driving in Costa Rica because most of the roads are only one lane, and if there is one car going slow the entire side of the road is held up.  Just be patient and pass with caution when you can see far enough ahead.  The Costa Rica government has recognized the traffic issues, especially on Sundays during summer. On Sunday afternoon/evenings in January, February, March, they close the entire westbound lanes of 27 and open them to all traffic going eastbound.  Our first night back in January, germany rental cars we got onto the highway and were so confused as to why everyone was driving on the other side of the road.  I was freaking out that another large earthquake had hit, but when we got back to Escazu we found out about the highway closure.