It is kind of funny, you can get across the country in about 5 hours, and that includes the slower speed limits and terrible road conditions!
Been there, went from San Jose to Puerto Viejo, was quite an adventure.
I found that the roads varied from surprisingly good to laughably bad (especially in the mountains).
If you want to go exploring, having a 4WD vehicle with a winch is not a bad idea. The first time I went, I was on a tour bus winding around steep mountain passes with what looked like about 6 inches to spare and no guardrail. One rediscovers prayer at such moments.