If you did not sign up in advance, it's not a problem since you can book shore excursions after you get aboard ship.
The roads in Costa Rica are in similar condition to what you would expect in rural America -- two lanes, reasonably maintained (but not perfect), and tending to twist and wind in mountainous terrain. The country is an oasis in the midst of its neighbors, and much less poverty-stricken. The people did seem friendly and, at least in the tourist area, genuinely honest.
In view of the distance to all of the attractions and the fact that you will see a great deal of the countryside when you transfer to or from the airport, you might want to consider skipping the excursions completely and just walking ashore in Puntarenas. The town's cruise ship pier is a new addition, so most of the shops apparently have not gotten into the typical "tourist trap" mode yet. Thus, it's a relatively normal Costa Rican fishing village. I know that's where I'm headed whenever I return there.