I have to disagree with Doakes on renting a car. The roads are dangerous, especially if you drive like the Ticos and pass regardless of oncoming traffic! The cost is high (but not necessarily as high as $100 day). I had good service when I rented a Toyota 4 runner from National near the airport on two trips last year.
A rental car gives you a lot more freedom to see and do things than flights and buses (And there is a lot to see and do in CR).
The Hampton is THE perfect place to stay if you arrive too late to drive to your destination before dark. Car rental lots are just a few hundred yards up the street. DON'T drive in CR after dark. I tried it ONCE and almost drove into a ravine that was where my side of the road was supposed to be.
My favorite place to go in CR is the Arenal volcano area, where you can see hot lava tumble down the side of the volcano from your hotel room on clear nights. There are also occasional explosions of ash.
We visited several national parks and preserves to see wildlife including sloths, three types of monkeys, scarlet maccaws, snakes, coatis, crocodiles, leaf-cutter ants, and much more.