Both road infrastructure and rules are not on par with American and European standards, so be prepared to stay focused on the road and drive defensively. Due to rugged terrain, curvy single lane roads, and slow moving trucks, it will take you longer to get most places than the actual distance would seem to indicate.
The advantage, though, of having a rental car is that you can jump in your vehicle and go exploring, grab a bite to eat, or head off on a side trip whenever you feel like it. With cell phone and GPS rentals offered by many companies, you can feel more connected and organized throughout your entire journey. With a good map or directions, you will save an enormous amount of time then, say, traveling by public bus.
There are, however, some disadvantages to renting a car. Because the roads and signs are of poor quality, it can be difficult to find your way around, especially if traveling at night. If you do get lost, you shouldn't have trouble finding someone to give you directions, although they will most likely be given in Spanish and the distances will be based on landmarks and given in kilometers.
Something to keep in mind is the price of gasoline, which is more expensive than in the U.S. and will be a significant expense, especially if you plan on driving all over the country.
Still, if you are determined to rent a car, remember these precautions: avoid driving at night, always lock your car, don't leave valuables in the car, and don't park your car on the street in large cities like San José, Alajuela, Puntarenas or Limón - rather, try to park your car in a secure lot with an attendant.
An alternative to renting a vehicle is to reserve shuttles or private transportation. For both options, a fully insured, recent-model minibuses (Toyota Hi-Ace van or similar) with air conditioning and a fully licensed and insured driver is utilized. Arranging for either of these options allows you to sit back, relax, and enjoy the ride.