Thanks for the tip!
My beer addled description made it sound like I was lumping Arenal and Tamarindo together though. Arenal is a nice area (mountainous, wet, green and cool like ireland) though there is not much of a town nearby. Tamarindo is an OK beach but as I said it seems to be a hangout for US hippies who don’t seem to care much for the town. There are some nice B&Bs outside of the town center though.
Roads in Costa Rica are riddled with potholes. If you book a rental car in advance you will probably want something with a good suspension and clearance.